RARE EARTH
THE ART AND SCIENCE OF CHINESE STONES
This exhibition is co-organized by the Crow Museum of Asian Art of The University of Texas at Dallas and the Center for Asian Studies of The University of Texas at Dallas, in partnership with the UT Dallas Department of Geosciences and the Dr. Robert Lavinsky Mineral Collection.
GEOLOGICAL SCIENCE INFORMATION
Emerald (mineral): Emerald is the gemstone variety of the common mineral Beryl (chemical formula Be3Al2(SiO3)6). Emerald’s deep green color reflects trace amounts of the element chromium or sometimes vanadium. Beryl has a hardness of 7.5–8 on the 10 point Mohs scale (talc = 1, diamond = 10). Beryl forms by heating and squeezing in the crust as a result of metamorphism. Gold (mineral): Gold is a chemical element with the symbol Au (from Latin: aurum) and atomic number 79, making it one of the heaviest elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile metal in a pure form. Gold is one of the least reactive chemical elements (it doesn’t combine with oxygen to tarnish or rust) and is normally solid. Because of its scarcity and chemical inertness, gold was one of the first metals used by humans. Gold often occurs in free elemental (native) form as veins associated with plutonic igneous rocks or as nuggets in sediments, eroded from veins. Sandstone (rock): a clastic sedimentary rock. Most sandstones are composed of sand-sized grains of quartz and many have a lot of vacant “pore” space between grains. These pore spaces allow fluids to circulate through the rock, sometimes leading to diagenesis. The large sandstone from Jinhai Lake on view in the exhibition is a good example of sandstone diagenesis. Silver (mineral): Silver is a chemical element with the symbol Ag (from the Latin argentum) and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal. The metal is sometimes found in veins associated with plutonic igneous rocks in the pure, free elemental form (“native silver”), as an alloy with gold and other metals, and as parts of other minerals. Quartz (clear) (mineral): Quartz is a hard, crystalline mineral composed of four silicon atoms combined with four oxygens. The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral in Earth’s continental crust, behind feldspar. Window glass is mostly made of silicon dioxide; like window glass, quartz is clear when there are no trace impurities. All quartz, colored or clear, has a hardness of 7 on the Mohs scale. Quartz (colored) (mineral): Quartz may be colored if there are trace amounts of metal such as iron incorporated in the mineral structure.
Hemimorphite (mineral): Hemimorphite is composed of zinc, silica, oxygen, and water, with the chemical formula Zn4(Si2O7)(OH)2-H2O. It is formed by the nearsurface oxidation and hydration of Zn sulfide ores. It has a Mohs scale hardness of 5. Aragonite (mineral): Aragonite is the orthorhombic variety of Calcium carbonate (CaCO3), the other is the trigonal variety calcite. Aragonite forms in sedimentary rocks and sometimes as cave deposits. It has a Mohs scale hardness of 3.5–4. Spessartine Garnet (mineral): Spessartine is a variety of garnet with the chemical composition Mn²+₃A1₂(Si0₄)₃. Spessartines are colored orange and have a Mohs hardness of 6.5–7.5. Pyrite (mineral): Pyrite is a brass-yellow mineral with a bright metallic luster. It has a chemical composition of iron sulfide (FeS₂). Pyrite is the most common sulfide mineral and has a Mohs hardness of 6–6.5. Turquoise (mineral): Turquoise is an opaque, blue-to-green mineral that is a hydrated and oxidized phosphate of copper and aluminum, with the chemical formula CuAl6(PO4)4(OH)8·4H2O. It is formed by the near-surface oxidation and hydration of Cu sulfide ores. It has a Mohs scale hardness of 5–6 Soapstone (rock): Soapstone is a rock composed mostly of the magnesium-rich mineral talc. It forms by metamorphic processes. Talc is the softest mineral (Mohs scale hardness = 1) so soapstone is also very soft. Calcite (mineral): Calcite is the trigonal variety of CaCO3. Calcite is found as the dominant component of the sedimentary rock limestone and metamorphic rock marble. Calcite has a Mohs scale hardness of 3. Marble (rock): Marble is a limestone that has been metamorphosed. It is mostly composed of the mineral calcite (CaCO3). Calcite has a Mohs scale hardness of 3. Jasper (rock or mineral): Jasper is a colored aggregate of microcrystalline quartz and is usually red, yellow, brown or green; the common red color is due to the presence of significant oxidized iron (Fe3+). Jasper has a Mohs scale hardness of 6.5–7. Copper (mineral): Copper is a chemical element with the symbol Cu (from Latin: cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. Copper is rarely found in its native state and is usually found in ore deposits associated with plutonic igneous rocks combined with iron and sulfur to make chalcopyrite (CuFeS2) or with oxides and hydroxides to make malachite, azurite, and turquoise. Copper metal has a Mohs scale hardness of 3.5.
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Malachite (mineral): Malachite is a copper carbonate hydroxide, with the formula Cu2CO3(OH)2. This opaque, green-banded mineral forms by the near-surface oxidation and hydration of Cu sulfide ores. It has a Mohs scale hardness of 3.5–4. Azurite (mineral): Azurite is a soft, deep-blue copper-bearing mineral produced by weathering of copper sulfides. Azurite has the chemical formula Cu3(CO3)2(OH)2. Both azurite and azure are derived via Arabic from the Persian lazhward, an area known for its deposits of another deep-blue stone, lapis lazuli (“stone of azure”). Azurite has a Mohs scale hardness of 3.5–4.
NEPHRITE
JADEITE
Jade is a monomineralic rock composed of fine aggregates of one of two different minerals: nephrite and jadeite. Nephrite is an amphibole (tremolite), with the chemical formula Ca2(Mg,Fe)5Si8O22(OH)2. Jadeite is a pyroxene, with the chemical formula NaAlSi2O6. Both are unusually tough and resist fracturing. Jadeite is generally harder than nephrite, with Mohs scale hardness of 6.5–7 for jadeite and 6–6.5 for nephrite. The surface of Jadeite is more glassy, whereas that of Nephrite is more waxy. Colors range widely, from iron-poor varieties, which are pale, to iron-rich varieties, which are green to deep green. Information provided by Dr. Robert Stern, Professor of Geosciences in the School of Natural Sciences and Mathematics, and Director of the Global and Magmatic Research Laboratory at The University of Texas at Dallas.
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