How to identify minerals with the naked eye

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Natural gold: usually appears as dispersed granules or irregular dendritic aggregates. It is golden in color, gradually turning into a pale yellow as the silver content in its composition increases. The streak is the same color as the body. It has a strong metallic luster. Hardness 2.5–3. It has high ductility and can be hammered into gold foil. The specific gravity of pure gold is 19.3. It has good electrical conductivity and good chemical properties; it is insoluble in any acid except aqua regia. Melting point 1062°C. Used for currency, manufacturing precision instruments, and decorations. It is mainly found in quartz veins, and natural gold often accumulates to form alluvial gold deposits. Diamond: It has an octahedral or rhombohedral crystal shape; the cubic form is less common, and it usually occurs in granular or fragmented forms. Colorless and transparent, or with blue, yellow, brown, and black hues. Standard adamantine luster. It has strong dispersion. Hardness 10. Brittle. Specific gravity 3.50–3.52. It exhibits yellow, green, and purple fluorescence under ultraviolet light. Used for precision and special cutting tools, drawing dies for manufacturing metal wires, drills, and precious gems. It is commonly found in kimberlites (i.e., brecciated mica peridotites) derived from ultrabasic rocks. When diamond-bearing rocks are weathered, diamond sand deposits can form. Kaolinite: Often appears in earthy, powdery, or flaky forms. The Pure ones are white in color; if impurities are present, they take on colors such as light yellow, light gray, light red, light green, and light brown. Waxy luster. The hardness is extremely low, 1–3 degrees. Specific gravity 2.6. It has strong water absorption and is sticky to the tongue. It is an important chemical raw material for ceramics, papermaking, rubber, and other industries. Kaolinite can originate from clay deposits, or from the weathering of feldspar, nepheline, and other minerals. Apatite: The single crystals are hexagonal columnar or thick-plate-shaped, while the aggregates appear in massive, granular, or nodular forms. Its color varies depending on the cause; pure forms are colorless or white, but these are rare. It is generally yellow-green, but can also be gray, green, brown, blue, purple, and other colors. Oily luster. It is mainly used in the production of phosphate fertilizers as well as various phosphates and phosphoric acids in the chemical industry. Marine sedimentary origin phosphorites possess great economic value. Sometimes associated with igneous rocks, they may also have economic value. Magnetite: It usually appears in granular or compact massive forms, with crystal shapes of small octahedra and rhombohedral dodecahedra. It has an iron-black color with a semimetallic luster. Hardness 5.5–6.5. It is brittle and has strong magnetism. It is an important iron ore. It is formed through endogenic and metamorphic processes. Pyrolusite: usually appears in grape-like, stalactitic, dendritic, and earthy aggregates. Grayish-black to black, streaks brownish-black to black. Semi-metallic luster; those that are earthy in appearance have no luster. Hardness 4–6. Brittle. Specific gravity 4.4–4.7. To extract important mineral raw materials for manganese. It is commonly found in sedimentary manganese deposits and the oxidation zones of manganese ores. Chalcopyrite: usually in compact massive form or as dispersed granules. Brass color. Streak is dark green with a metallic luster. Hardness 3–4. Brittle. It has a specific gravity of 4.1–4.3 and is conductive. It is an important mineral raw material for copper extraction. Chalcopyrite can form under various geological conditions. Galena: The crystals are often cubic in shape, and they typically form granular or compact massive aggregates. The color is lead gray. Streaks are gray-black. Metallic luster. Hardness 2–3. It has a high specific gravity, ranging from 7.4 to 7.6. It has weak electrical conductivity and good detection properties. It is the most important mineral raw material for lead extraction, and often contains silver and zinc as by-products. It is widely distributed in nature; hydrothermal processes are the most important, and it often forms sulfide deposits together with sphalerite. Zinc blende: Its crystal forms are often tetrahedral or rhombohedral, but the more common form is granular masses. The color varies depending on the iron content, ranging from gray, light yellow, brownish to black. Streaks are white to brown. The gloss ranges from resinous to semimetallic. From transparent to translucent. Hardness 3.5–4. The specific gravity ranges from 3.9 to 4.1, and decreases as the iron content increases. Sphalerite is an important mineral raw material for zinc extraction, and elements such as cadmium, indium, and gallium can be obtained from it. It is commonly found in hydrothermal deposits. Wolframite: Often appears in plate-like and granular forms. Color is brown to black. The streak is dark brown. Semi-metallic luster. Hardness 4.5–5.5. Specific gravity 6.7–7.5. Those with higher iron content exhibit weak magnetism. Wolframite is an important mineral raw material for the extraction of tungsten, and it is mainly used in the smelting of alloy steel and in the electronics industry. It is commonly found in high-temperature hydrothermal quartz veins and granite-associated deposits. Cassiterite: Its morphology varies depending on the formation temperature, crystallization rate, and impurities it contains. The crystals are often bipyramidal-prismatic, elongated prismatic, or acicular in shape, while the aggregates appear as irregular granular masses. It is generally reddish-brown; colorless variants are extremely rare, while those containing tungsten appear yellow. The streak is pale yellow. Diamond luster, greasy luster on the fracture surface. Semi-transparent to opaque. Hardness 6–7. It is brittle, with a conchoidal fracture, and has a specific gravity of 6.8–7.0; it is the main mineral raw material for tin extraction. Its formation is closely related to granite; cassiterite quartz veins of vaporization-high-temperature hydrothermal origin are the most valuable, and after weathering, they often become concentrated as tin ore sand. This post was last edited by The distance to happiness on 2009-4-5 09:36.]