Precious: Has beauty, durability, size, and rarity.(Diamond, emerald, opal,ruby,safphire) Semi-precious: only two of those (quartz, Jade) A gemstone or gem (also called a precious or semi-precious stone) is a piece of attractive mineral, which when cut and polished is used to make jewelry or other decorations.
The Mohs Scale characterizes the scratch resistance of different types of minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German mineralogist Friedrich Mohs.
Most gemstones are hard, but some soft minerals are used in jewelry because of their luster or other physical properties that have value. Luster: the way light interacts with the surface of a crystal, rock, or mineral.Sheen. Adamantine Luster Adamantine minerals have the best lustre. It is mostly seen in diamond.Diamond minerals are transparent and refract the light the best.Minerals with a true adamantine lustre are uncommon. Dull Luster Dull (or earthy) minerals have little to no lustre, because they are coarse and grainy, which scatters light in all directions instead of reflecting it. These minerals are not used for jewlery or decorations. Greasy Luster Greasy minerals resemble fat or grease. A greasy lustre often occurs in minerals containing a lot of microscopic inclusions. Some examples are opal and cordierite.Many minerals with a greasy lustre also feel greasy or smooth. Metallic Luster Metallic minerals have the lustre of polished metal.
Pearly Luster Pearly minerals consist of thin transparent sheets. Light reflecting from these layers give them a lustre similar to Pearls. Resinous Luster Resinous minerals have the appearance of chewing gum chewing or plastic Submetalic Luster Submetallic minerals have similar lustre to metal, but are duller and less reflective Vitreous Luster Vitreous minerals have the lustre of glass. This type of lustre is one of the most commonly seen, and occurs in transparent or translucent minerals minerals have a luster resembling wax. Waxy luster Silky Luster Silky minerals have a parallel arrangement of fine fibers. This makes the minerals look like silk.
Magmatic Crystallization: Cooling Magma produces crystals of different kinds of minerals. Crystals are formed from the lava when the volcano erupts. Examples: moonstone, topaz and corundum. Pegmatite: Towards the final stage of magmatic crystallisation, a thin silicate liquid remains and if this is squeezed into surrounding rocks, it produces pegmatites containing very large crystals. Examples:Tourmaline, topaz, beryl, quartz and spodumene are some of the common pegmatitic gem stones. Metamorphic deposits: When a rock is in a high temperature and or high pressure, the chemical components get rearranged into new minerals. Gem minerals formed are diopside, corundum, andalusite, sillimanite, kyanite, epidote, and garnet.
moonstone, topaz and corundum kyanite, epidote, and garnet topaz, beryl, quartz diamond, ruby, sapphire
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