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University of British Columbia
Earth and Ocean Sciences
EOSC 118
Peter Mahon

1 3. Significant People and Groups Gold South Africa currently produces 11% of the world's newly mined gold (Chemical Symbol: Au) and has long been the world's largest producer of gold. However, in recent years China has produced slightly more gold per year (12%). Australia, North and South America all produce significant quantities as well, with Canada being the 8th largest producer in the world at 4% of the world's output. Most of the gold in Canada originates from hard rock mines in Ontario, Quebec, and British Columbia. The total global amount of gold produced on a yearly basis for the last five years averages ~2,500 tonnes. Jewellery production accounts for 83% of the global consumption of gold with the remainder being made up primarily by electronics, currencies and investments. On a company basis, Barrick Gold of Canada is the largest non-Chinese producer of gold amongst those that have publicly released their production data. It is responsible for approximately 10% of the market share, generated from 27 active mines on 4 continents. AngloGold Ashanti of South Africa (20 mines in 10 countries on 4 continents) and Newmont Mining of the United States (mines in 9 countries on 5 continents) each produce 7% of the world's new gold. These large companies can exert significant leverage across borders and their combined large numbers of operations have inevitably led to questionable situations (politically, socially, and environmentally) for each of them. "New Gold" is distinguished from "Total Gold" in global production number because a significant amount of gold is recycled or pulled from central stockpiles when demand is high. Platinum Group Metals (PGMs) Platinum (Chemical Symbol: Pt) is commonly found with five other similar metals in nature: palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir) and osmium (Os). They are rarer than gold, have a number of high-tech applications and less are produced annually. The price of each metal fluctuates according to industrial applications, but in general Rh is the most expensive, Pd is the least expensive and Pt has normally sat between the two. The graphs at the end of this page show plots of historical prices for the platinum group elements. The PGMs have a higher melting point than gold and exhibit very good durability and strength. Use in jewellery accounts for approximately 30% of the global consumption of platinum and palladium with the rest going primarily to autocatalysts (with 15% into electronics). The market for platinum sales is a free market and prices of PGMs are largely dictated by the global supply balanced by the demand in the autocatalyst and jewellery markets. With a global supply of platinum group metals on the order of 475 tonnes (or ~17 million ounces), and much of that coming from the South African Bushveld Region, PGM prices are subject to large swings especially if conflict slows or halts production in South Africa. The two main producers of PGMs are South Africa (79%) and Russia (12%), with significant tonnages provided by the US (2%) and Canada (4%). The total annual output of Pt and Pd in 2005 from all mines was 216 and 214 tonnes, respectively, with about 23.5 tonnes of Rh produced as well. In South Africa, the Bushveld Complex is the primary geologic structure that hosts the mines that are producing the majority of the PGMs. Minor contributions come from Palabora and the Witwatersrand Basin. Canada's production comes largely from the Lac des Iles operation near Thunder Bay and as a secondary product from the Sudbury Complex's nickel deposit in Sudbury, Ontario. The Stillwater Complex is the primary resource of the United States. Anglo Platinum Group Ltd. is the largest producer of platinum with several operations in South Africa and Canada. Diamonds When one thinks of diamonds, the name De Beers immediately comes to mind, and with good reason. De Beers Consolidated Mines Ltd. has essentially controlled the entire diamond market since its inception in 1888 with the Kimberley Mine in South Africa up until the last two decades. In addition to controlling the movement of diamonds from most mines through the central Diamond Trading Company (DTC) and global network of Sightholders and Diamond Bourses, De Beers has also conducted very successful marketing campaigns and kept prices high for this tightly 2 moderated commodity. As demand from consumers varied through time, so has the limited release of diamonds to retailers even though supplies from diamond mines has remained quite high at times. The following is a typical, but generalized, view of the steps involved in bringing a diamond to the market: 1. Geological prospecting and exploration 2. Mine development and mining 3. Sorting, valuing, and sighting of rough stones (DTC) 4. Cutting and polishing into finished diamonds 5. Jewellery manufacturing and distribution 6. Retail stores and sales 7. End consumer Once diamonds have been found (step 1) and are then pulled from the ground in the mining step (2), they are sorted into gem, near-gem and non-gem parcels. In step 3, the Diamond Trading Company coordinates delivery of raw goods from the mine to optimized parcels for Sightholders. Within these parcels are also divisions based on size, colour, and clarity of the rough diamonds. These packages are called 'sights' and their sales are tightly monitored; only registered Sightholders are normally allowed to purchase sights. It is difficult to value rough diamonds and there are not necessarily any fixed formulas to determine this. Once the parcels have been bought, the rough diamonds are then faceted and transformed into what we as consumers usually encounter - polished gemstones (step 4). There are a number of 'cutting houses' around the world, but some of the historical centers are in Antwerp, Mumbai, New York and Johannesburg. Lower cost cutting facilities have become more common and are located in places such as India, Thailand, and China. Jewellery manufacturing happens on both large and small scales. Some of the larger retail outlets have their own manufacturing arms. However, most retail outlets are 'independents' and source their finished products from manufacturers around the globe. Each manufacturer will typically have a specific target clientele in which they design their jewellery for (e.g., middle class consumers or high end luxury brands). Exceptions to this chain of custody, however, have changed the way diamonds have moved from mine to market. De Beers' strong control of the global diamond trade began to diminish with the establishment of Australia's Argyle Mine in the 1980's. The Argyle Mine was not owned by De Beers and although it ran some of its large production of diamonds through the central Diamond Trading Company, much of their material bypassed this conventional port to the consumer. Political changes and the deregulation of diamond distribution in Russia (due to political collapse) and Angola (due to abundant small scale diamond production) in the early 1990's also delivered a large blow to the DeBeers control. In the late 1990's the first diamond mine in Canada, Ekati (operated by BHP Billiton), started to bring more high quality material to the market but also not through De Beers. In 2003, Rio Tinto opened Canada's second diamond mine, Diavik, followed by Tahera Diamond Corp's Jericho Project that started production in 2006. By the end of 2007 these three diamond mines in Canada were already providing 12% of the global production of diamonds with a value of ~Can$1.7 billion. The monopoly on the diamond market by De Beers is now effectively gone. However, the tight control of diamonds on a global scale continues with the aid of the Kimberley Process. The diamond market is now more competitive but because of the huge amount of money invested in creating this industry, the flow of finished goods to the consumer is still tightly controlled but just not from one individual company now. Of all the diamonds being mined only about 20% actually end up being of good enough gem quality to turn into polished goods. And of that 20% considerable loss is incurred when a diamond is taken from its rough form and turned into a finished gemstone. The remaining 80% of the non-gem diamonds are used in industrial applications. These non-gem diamonds are often called bort and exploited for their phenomenal physical properties. The most common use for these diamonds is as abrasives. 3 Retailer and Industry Organizations An important part of the diamond and jewellery industry is independent evaluations and training of certified gemologists. An independent evaluation of diamonds is significant because small differences in the grade of a diamond (e.g., between a D and F coloured stone) can be substantial. If a retailer is selling a stone, they may wish to 'upsell' the quality of a diamond, whereas the consumer would prefer to 'downsell' the diamond. An independent evaluation of the stone in question eliminates these aspects and protects both the consumer and the retailer. Various laboratories conduct evaluations, or certification, of a diamond but in North America, the Gemological Institute of America (GIA) is the most reputable and most stringent diamond grader. Other labs include the International Gemological Institute (IGI), American Gem Society (AGS), and European Gemological Laboratories (EGL). All of the reports generated by the above organizations will include documentation of the cut quality, colour, clarity and carat weight of the investigated stone. Physical dimensions of the stone are also recorded and enhancements to the diamond are also recorded along with any information pertaining to the stone's origin. Retailers and manufacturers have created organizations to form a collective voice for the industry and provide functions and forums for collaboration and discussion of current topics. The American Gem Trade Association (AGTA), Canadian Gemological Association (CGA), Canadian Jewellers Association (CJA), and Jewelers Circular Keystone (JCK) are all groups that provide benefits to their members. Many of these groups, along with the GIA and AGS also offer educational programs where students may learn the techniques required for certified gemological testing. For example, the GIA offers a Graduate Gemologist Diploma Program that is highly respected in the gem and jewellery industry. Auction Houses and Luxury Brands When we discussed famous gemstones and jewellery in the previous Lesson it was apparent that polished diamonds over 50 carats were highly unusual and did not follow the conventional path of being sold from a retailer to a consumer. Your mid-range and high-end jewellery stores will often carry stones up to 15 carats in their jewellery selection, but pieces over that size are often in cases mostly for show rather than as regular pieces. So where does one acquire fantastic stones or pieces of jewellery that don't reside in castles and in Royal Vaults? Luxury and high end auction houses. The two most renowned auction houses are Christie's and Sotheby's whose auction lots include magnificent gemstone and jewellery pieces. These pieces are routed through these companies for sale; this is where record prices are typically set for gems and jewellery. Many luxury brands exist in today's market, however, many more have faded away in the past. Only a few have survived long enough to become household names across North America. Tiffany & Co. , Harry Winston, Inc. and Van Cleef and Arpels are synonymous with exquisite luxury jewels. Each has claims to fame and have played important roles in the jewellery industry by adorning the wealthy and famous with magnificent jewels. Tiffany & Co. was founded in New York in 1837 and is well associated with "The Tiffany Diamond", a 128.54 carat fancy yellow diamond. Harry Winston was an entrepreneur born in the late 19th century and started a very successful jewellery company in the US. A work of note by Winston are the 12 Jonker gems. He also dealt with creating jewellery for dozens of large diamonds and was involved in the buying and selling of famous pieces (such as the Spanish Inquisition Necklace) throughout his career. Harry Winston has also donated many stones to the Smithsonian Institution (e.g., the Hope Diamond and the Oppenheimer Diamond) and helped create one of the most fantastic publicly owned gemstone collections in the world. Van Cleef & Arpels was founded in 1896 in Paris, France, and served much of the European elite. Examples of their work include the Princie Pink Diamond Pendant and the Empress' Crown of the Iranian Crown Jewels. 4 4: Current Trends and the Media Significance of Gems and Precious Metals in Society Gems and jewellery have been intertwined with humans and religion for thousands of years and have played significant roles throughout antiquity. These treasures have been largely reserved for the wealthy and influential as symbols of power but also as amulets to tap into their inherent mystical properties. They have been used as royal gifts and official seals, and today many fantastic jewels of the world sit on display for public viewing. Precious metals and gems, especially diamonds and gold, have also been used as currencies and financial investments in one way or another. Furthermore, the value and importance of gems and precious metals often transcended political and religious borders, indicating that most societies appreciate and value them for similar reasons. "Rankings" of gems and metals may differ from group to group, but the intrinsic beauty and value of certain materials is undeniable, as is the case with gold. This material has been incorporated in almost all societies and its discovery was likely made independently in many of the ancient civilizations. Its resistance to corrosion, beautiful colour and malleable nature has allowed this material to form the heart of much valued jewellery and religious items. Today, many of the historical principles by which gems and precious metals earned their respect continue to underlie the variables that define their current value. Of course, things have changed a bit. Modern exploration and mining practices coupled with increased diversification of global wealth has generated a significant market accessible to individuals other than royalty and the ultra-wealthy. This has been effectively accompanied by clever marketing, especially in North America, that has driven the demand level dramatically since the early 1900's. The increase in demand has increased production, and therefore brought prices down considerably based on economies of scale. Precious gems and metals have also been used as international standards for which to value national currencies against. The 'gold standard' was officially abandoned in only 1971, and economists around the globe closely monitor the precious metals industry for their clients, who range from individuals to large pension funds as well as governments. The value of these precious metals fluctuates with global economic conditions. For example, instability in the major countries and major metal producing countries can cause dramatic prices changes. For example, gold has reached local peaks over 1000 USD per ounce in March 2008 and February 2009, and continues to be very highly valued today. "Red Carpet" Events and Celebrity Styles Many of us in North America have our own collections of jewellery and gems but we are always looking to the wealthy and famous to be impressed. Hollywood, and now increasingly Bollywood, has been used as a stage to advertise and promote specific lines and brands of jewellery as well as to market specific commodities. The stars of the stage are always adorned with fancy and expensive jewellery that only the top tier could afford, but often they don't own the jewellery they are wearing – it's borrowed! Designers and high end jewellery houses commonly lend out extravagant pieces for big events because there is no better publicity for their jewellery than being worn by a star that is receiving an award! At the 2009 Golden Globe Awards much of the fine jewellery flaunted at the Red Carpet event included Red Stones, with a few diamonds and turquoise stones mixed in for diversity. Kate Beckinsale wore red chandelier-style red spinel and diamond earrings designed by Fred Leighton while Julia Ormond also sported red in Neil Lane-designed earrings encrusted with red garnets. J-Lo wore a large ruby ring with diamonds designed by L. Schwartz while Blake Lively was seen with a carved ruby, sapphire and diamond bracelet designed by Fred Leighton. Eva Mendes was adorned with a necklace from the Van Cleef & Arpels collection that was originally made in the early 1970's. The piece was made in yellow gold and featured 132 individual and well matched turquoise stones accented by fine white diamonds totaling more than 36 carats. Along with the beautiful necklace were diamond earrings set in white gold. A second actress sporting Van Cleef & Arpels was Anne Hathaway who wore a set of 1930's sapphire and platinum earrings that matched an 18 karat white gold ring with a spectacular 13 carat sapphire. Marketing of major brands has also been injected directly into motion pictures for quite some time: "Bride Wars" (a 2009 motion picture) clearly features Tiffany & Co. and their line of engagement rings, "Breakfast at Tiffany's" (from 5 1961) features Audrey Hepburn at the same luxury jewellery brand's store, and the 1953 film "Gentlemen Prefer Blondes" has Marilyn Monroe singing "Diamonds are a Girl's Best Friend". Historical events can be very influential to the jewellery industry. Michelle Obama created a bit of a stir during Barack Obama's inauguration in the United States with her stylish jewellery selection. The Loree Rodkin-designed "Triple Constellation" diamond chandelier earrings she was wearing were studded with small diamonds and constructed of 18 karat white gold. Demand for similarly styled products increased dramatically following Obama's victory. Designer Loree Rodkin has likely seen an increase in demand for her pieces and other jewellery artists are sure to take notes from this influence on US trends. Arts and Design Competitions Like in many arts circles, design competitions and exhibitions for jewellery and gems are held to showcase a region's best artists, as well as to draw artists from around the globe. One excellent competition is "AuDITION", which is sponsored by the World Gold Council and AngloGold Ashanti. This competition focuses on innovative jewellery designs specifically in high-karat gold. The location of the competition changes regularly and effectively brings current designs from many different global cultures. Recent events have been held in Brazil, South Africa, China, and India, with all winning designs compiled on their central website. The American Gem Trade Association (AGTA) hosts a well-known design competition in North America. That design competition is aimed primarily at the US custom-jewellery market and awards are given for a number of different categories including "Platinum", "Consumer's Choice", "Pearls", "Fashion", "Manufacturing", and "Cutting Edge". The "Cutting Edge Awards" are particularly interesting because of their focus on innovative and creative lapidary arts (or gem faceting). Consumer Trends and Corporate Responsibility As much as gold and gems have been at the heart of precious items historically and through to high profile Hollywood events, today's consumers are driven by different concerns from those of even 10 years ago. People demand to know where their jewellery came from and what impact it has had on the lives of people involved in its production and on the land from which it originated. For example, the movie "Blood Diamond" that widely hit the screens in 2006, retrospectively publicized the existence of diamonds that originate from zones of conflict and that were used to fund the continuation of those wars. A few years prior to the release of the movie "Blood Diamond", the Kimberley Process, an industry-driven set of regulations, was voluntarily adopted by the majority of the diamond producing and consuming countries of the world in a fight to quench the trade of illicit diamonds. In addition to being more aware of the potential illicit nature of diamonds, the savvy consumer with access to the Internet's vast information (and misinformation) also started to become concerned with the sourcing of the precious metals and other gemstones in jewellery. While the mining impacts of diamonds from their host rock (kimberlite) is relatively low, the extraction of gold and other precious metals from the ground can have much more significant impacts. If mining of precious metals is done without corporate, social, and environmental responsibility, serious environmental and social damage can occur. The National Geographic Magazine article, which you may want to read, documents some of the negative impacts of gold mining in several countries and also looks at where the main global consumers are located (see link above). Initiatives working towards responsible practices include the Initiative for Responsible Mining Assurance (IRMA) and the Responsible Jewellery Council (RJC). In certain cases embargoes have been placed on products with questionable origin, as was the case with Burmese gemstones (mostly rubies and jade) that were originally banned from importation into the USA in 2003. Sourcing "green" and "certified" products is also a current trend and is linked directly with assessing the full story behind each piece of jewellery for sale. "Green" products in the precious metals and gems world have largely been dominated by recycled materials, either from remelting of old pieces or simply reusing antiques. Non-metal and gemstone alternatives are also becoming more popular, as in the case of imitation coral. Certified products are those that have a specific origin and can be tracked back through their chain of custody to ensure that proper social, environmental, and corporate responsibility have been integrated into creating the product. The Kimberley Process is a 6 very good example that covers an entire gemstone product and associated industry; similar processes are being done on a smaller scale for other gemstones and brands. Partially prompted by the surge of demand for certified Canadian diamonds, this country has also produced a number of corporate leaders in certifying their products. For example, Maple Leaf Diamonds and CanadaMark are certified as products of the Ekati and Diavik diamonds mines of the Northwest Territories. Products branded as "Certified Canadian Gold" ensures that all products with this stamp use only gold that has been mined and refined in Canada. There is also a voluntary code of conduct that many Canadian diamond producers, manufacturers, distributors, and retailers follow that goes beyond the requirements outlined by the Kimberley Process. The internet has not only been effective at quickly disseminating information about some of the negative aspects of the gem and precious metals industry, but it has also allowed for a new form of retail to emerge. Online jewellery, precious metal and gemstone stores have popped up left, right, and center with variable success and reliability. Of the thousands of stores promoting their product the most reliable companies are those with physical locations and longer histories. Issues arise for online consumers because it is easy for dishonest people to pass off imperfect or lesser stones to an uneducated and anonymous buyer. Retail jewellery stores with physical locations in malls or elsewhere would have a hard time doing this and dishonesty would quickly come back to them if caught taking advantage of the consumer. The price points for consumers considering buying online are actually fairly similar to what you would see today in a retail store within your community, except that you lose out on the personal face-to-face interaction with trained staff and associated customer service (such as ring sizing). Blue Nile, however, is an example of a company that is selling diamonds and jewellery online in an honest and secure manner. On their website, internet users can quickly compare diamonds of different sizes, shapes and quality all from their home computer and the service has been reviewed by magazines such as Forbes, The Economist, and BusinessWeek. 7 5: Key Geoscience Concepts The word "Science" What follows is an uninspiring dictionary definition of science: "Branch of Knowledge, especially one dealing with material phenomena and based on observation, experiment and induction; systematic and formulated knowledge; pursuit of this; skillful technique." The field of science is very exciting with new discoveries being made each day with inextricable links to past ideas - an interweaving of new observations with historical data and interpretations. To some it can be a discipline filled with math and rambling facts with very little relevance to modern day life. It is our hope that we can turn this perception around with the exciting world of gemstones and precious metals and show you that science is a dynamic process of discovery and exploration involving the integration of many disciplines from both the sciences and the arts. Hopefully you will be able to appreciate science when it sneaks its way into many aspects of your daily life: from the ring on your finger, to gold wiring in your cell phone, to the latest fashion trends in Hollywood! Earth System Science In Earth Sciences the integrated approach to study is called "Earth System Science". Earth System Science views the Earth as a working system, each part having an impact and an effect on the other. The figure below attempts to illustrate this new way of looking at the Earth. In order to understand how the Earth created/creates beautiful and inspiring gems and metals, we must appreciate all aspects of the Earth system including the atmosphere, oceans, surface tectonic processes, processes deep in the Earth, and life. The significance of these components will vary for the creation and preservation of different precious materials, but all aspects tend to be tied together in one way or another. Diamonds, for example, form deep within the Earth in a region called the Upper Mantle where very high pressures and temperatures exist. However, other processes are required to bring these diamonds through the mantle and crust to the surface in order for us to find and eventually mine them. Natural processes on the Earth's surface, such as glaciation, can move the diamonds away from their original source and leave a "cookie crumb trail" to where the real treasure lays (the 'primary deposit'). Alternatively, if enough diamonds were moved by natural processes (e.g. fluvial transport) from a 'primary source' to a new location, a 'secondary' diamond deposit would be formed far away from the original source. Even in this very limited example, the complexity and "interconnectedness" of the Earth system is obvious. Get ready to explore many more complex systems that exist within the gem and precious metal world! The Scientific Method At the core of scientific investigation is the scientific method. Science is not a faith or belief system but a method of observing and attempting to interpret the physical universe. As such, science holds that every event has a physical explanation. The traditional process of scientific investigation involves a number of rigid steps: 1. Compile observations: Making detailed unambiguous and clear observations is vital to any scientific investigation whether that is recording results in a laboratory or describing the geology and mineralogy of a diamond-bearing rock. 2. Form a Hypothesis: This is a provisional theory to explain the observations made. We might first consider that the rock that contains the diamonds is what geologists call kimberlite. 3. Test the Hypothesis: For our diamond example, a way of testing if the rock is truly kimberlite is through the other minerals that exist in the rock. 4. Repeated testing raises the hypothesis to the level of a Theory. As such a theory is not a 'guess' but something that has been tested in many different ways and found to be true after each testing. 8 5. If a Theory or group of theories are always observed to happen it could be raised to the level of a Law. An example is the "Second Law of Thermodynamics", which states that heat flows from a warm body to a cooler body. 6. Continual re-examination. In science, everything can be tested and reinterpreted, even Laws! For example, some of the laws proposed by Isaac Newton have subsequently been called into question by the recent development of Quantum Theory. In reality, however, this process is much too rigid and simple to be easily applied today. The principles and concepts that it conveys are valid, such as objective testing and interpretation, but the manner in which researchers navigate their experiments, data, and conclusions tends to be more flexible, creative and iterative. The following (optional) website includes a great Flash animation describing one representation of "The Scientific Method", or rather, "The Real Process of Science". Earth's Interior One of the features of our planet is that it is not homogeneous but rather composed of a number of very distinct solid layers. These layers, from the exterior to the interior, are: Lithosphere. The lithosphere consists of continental and oceanic crust and the uppermost part of the mantle. This layer is fractured into a number of rigid sections or plates. Continental crust and oceanic crust have different overall compositions; continental crust is much richer in minerals containing silicon (Si) while oceanic crust has a higher iron (Fe) content. Continental crust also tends to be much thicker than oceanic crust. Asthenosphere. The upper mantle material acts as a relatively soft, lubricating layer over which the crustal lithospheric plates move. Mantle. A relatively hot viscous "taffy-like" layer. The mantle is in continual motion with hot mantle material rising from the depth and cooler upper mantle material sinking to the lower areas. These motions are called convection currents and may in part help drive the motion of the lithospheric plates. Next time you are eating Miso soup, check to see if you can see the convection currents! Outer core. This layer is a liquid. Inner core. This layer is a solid and has a metallic composition. Theory of Plate Tectonics The Theory of Plate Tectonics is often called the geological Grand Unifying Theory. It explains many of the geological phenomena that have puzzled scientists for so many years, such as the processes that build mountains and the patterns of distribution of earthquakes and volcanoes. The theory describes how the plates and the continents they contain are pushed and pulled around the surface of the Earth. The surface of the Earth resembles a fractured eggshell with each fragment of that "shell" (the Earth's crust) being a plate. In general, most geological activity (such as earthquakes, volcanic activity, and mountain building) that affects the surface of the Earth occurs at the plate boundaries whereas the central portions of the plates tend to be quite 'stable'. The three main types of plate boundaries are convergent, divergent, and transform. Divergent (Constructive) Plate Boundaries Tectonic plates move away from each other at these boundaries and new crust is produced ("constructed"). These boundaries can form within a continental plate to ultimately form a new ocean basin. An example of a constructive plate boundary is the Mid-Atlantic Ridge (MAR). This feature has been widening the Atlantic Ocean at an average rate of about 2.5 cm per year (this rate varies along its length). The MAR is notable in that it is one of the few that can be observed on land. Convergent (Destructive) Plate Boundaries At convergent boundaries, two plates move toward each other and collide. The Himalaya mountain range was formed when two continental plates, the Indian and Eurasian plates, collided (continental-continental collision). 9 When two oceanic plates or an oceanic plate and a continental plate are in collision, one plate is pushed under or subducted below the other. When two oceanic plates collide, a chain of volcanic islands develops above the zone of subduction. In the case of oceanic-continental plate collision, the oceanic plate is always subducted below the continental plate because oceanic crust is denser than continental material. In this case mountain ranges that run along the edge of a continent, such as the Cascades in North America, will be produced. Transform Plate Boundaries At transform boundaries the plates move past each other without the creation or significant destruction of crustal material. The most famous transform plate boundary is coincident with the feature known as the San Andreas Fault where the North American Plate is moving past the Pacific Plate. Crustal Thicknesses As alluded to previously, the thickness of the world's crust varies in time and space as geological processes incessantly march forward. The following image from the USGS is a map of the world with the thickness of the crust mapped out - each line traces areas of equal thickness as measured in kilometers. Roughly, the continents and their margins are outlined by the 30 km contour. Continental crust with a thickness greater than 50 km is rare and accounts for less than 10% of the continental crust! Gems, Rocks, and Minerals As a general statement, gems are valuable minerals that originated from an original source rock. However, the definition of the term 'gem' is in reality much more broad. A gemstone (the words gem and gemstone are commonly interchanged) is any mineral that is highly valued for its beauty, durability, and rarity. Included in the mineral-focused gemstone definition are non-mineral gemstones that are organic or biological in origin, such as pearls and amber. Ok then, so what is the difference between a rock and a mineral? Well, rocks can essentially be thought of as (i) naturally occuring aggregates of (ii) minerals. A lengthy definition (but concise at the same time) of the term mineral is as follows: "A mineral is a (i) naturally occurring (ii) homogeneous solid with a (iii) definite (but generally not fixed) chemical composition and a (iv) crystalline structure. It is usually formed by (v) inorganic processes" It is important to note that rocks and minerals are NATURAL, so if something is made by people in a lab or elsewhere, it is not a rock or mineral. We will come back to these items later, but it is important to remember since these parameters are what we use to classify and study rocks and minerals. And since most gems are minerals this classified way of looking at minerals allows us to easily differentiate a valuable ruby gemstone from common red glass! To finish off this activity, read pages 104 and 105 of your textbook that addresses the question of'What is a gemstone?' The Three-fold Rock Classification System The basic three-fold classification of rocks are igneous, metamorphic, and sedimentary. These rock types are related to each other via processes that change from one type to another over time. Our textbook expands on what is presented below about three rock types, be sure to have read the appropriate pages as indicated in the Introduction! 10 Illustrating the Rock Cycle. At A, extrusive igneous rocks form from magma that cools as it reaches the surface of the Earth. At B, Intrusive plutonic igneous rocks intrude from below the subsurface, cool, crystallize, and eventually are exposed by erosion at Earth's surface. At C, metamorphic rocks form as a result of the transformation of existing rock. At D, sedimentary rock forms from sediments such as chalk, limestone, dolomite, sandstone, conglomerate, and shale that are then compacted and converted to rock by the process of lithification. Igneous Rocks Igneous rocks crystallize (a process sometimes called solidification) from a molten material (called a meltor magma) to form a rock composed of interlocking crystals. The melt is generated from a process called "partial melting" of mantle material or of rocks deep in the crust. If this melt cools to form a rock at the surface of the Earth, it is called volcanic or extrusive. If the melt cools and solidifies inside the Earth it is called plutonic or intrusive. Metamorphic Rocks Metamorphic rocks are formed by the alteration of pre-existing rocks (igneous, metamorphic, and sedimentary) via metamorphism. The processes that transform or metamorphose rocks involve heat and/or pressure and very often fluids percolating through the subsurface. Rocks can be compressed and flattened and new minerals may be generated that are more stable under the new temperature and/or pressure conditions. Pressure is often the result of compressional tectonic forces generated when plates collide; this can also generate heat. In addition, pressure and temperature will increase with depth. Sedimentary Rocks Sedimentary rocks form by a number of processes and can generally be classified by:  Physical erosion and weathering of another rock to form a clastic sedimentary rock such as a sandstone, siltstone, or mudstone. These rocks are composed of the fragments and grains of the rock(s) that were being eroded to form the sediment.  Chemical precipitation to form an evaporite. These form when a body of water such as a lake or inland sea evaporates to form layers of salt.  Biological precipitation of minerals includes the production of coral reefs, sediments composed of shells, and deposition of plant material in swamps to form coal. 11 Sediments are transformed into rock via a process called diagenesis or lithification which physically cements the sedimentary grains together. Like metamorphism, this process involves heat, pressure, and percolating fluids but not to such a degree that the rocks mineralogy or structure is drastically transformed. The Rock Cycle The rock cycle describes how rocks can be transformed by various Earth processes into any other rock in the three-fold classification as illustrated in the figure below. Note that not every rock has to pass through each of the stages in the rock cycle. The Rock Cycle. Starting from the bottom: partial melting of mantle material forms magma; magma crystallizes to form igneous rocks; weathering and erosion of igneous and metamorphic rock produces sediments which lithify to form sedimentary rocks; some igneous and sedimentary rock undergo tectonic burial and metamorphism to form metamorphic rock. 1. Mantle plumes can add volatiles to the atmosphere during volcanism and degassing. 2. Solar energy drives surface processes. 3. Meteoric water (water originating from the surface) infiltrates the crust and alters rocks. These fluids may participate in igneous activity or metamorphism of rocks. On the surface, meteoric water may chemically or physically weather rocks. 4. Igneous activity includes both intrusive events and extrusive events. During these processes fluids are released into surrounding rocks and gases are released into the atmosphere if they reach the surface. 5. The biosphere hosts critters in the ocean and lakes that can precipitate biominerals as sediments, which can eventually become rocks. 6. Subduction occurs with the forceful downward motion of super positioned material to deeper depths as the result of tectonic forces. 7. Mantle mixing is thought to occur at the core-
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