Beryl BeࠣAlࠢSiࠦO₁ࠨ Chrysoberyl BeAlࠢOࠤ Coral CaCOࠣ Corundum AlࠢOࠣ Diamond C Feldspar Plagioclase Series: (Na,Ca)Al(Al,Si)SiࠢOࠨ Alkali Feldspar Group: Mixtures of Orthoclase—KAlSiࠣOࠨ and Albite—NaAlSiࠣOࠨ Garnet Almadine—FeࠣAlࠢ(SiOࠤ)ࠣ Andradite—CaࠣFeࠢ(SiOࠤ)ࠣ Grossular—CaࠣAlࠢ(SiOࠤ)ࠣ Pyrope—MgࠣAlࠢ(SiOࠤ)ࠣ Spessartine—MnࠣAlࠢ(SiOࠤ)ࠣ Uvarovite—CaࠣCrࠢ(SiOࠤ)ࠣ Jade Nephrite—Caࠢ(Mg,Fe)ࠥ(SiࠨOࠢࠢ) (OH)ࠢ Jadeite—NaAl(SiࠢOࠦ) Lapis lazuli Lazurite—(Na,Ca)ࠨ(AlSiOࠤ)ࠦ (SOࠤ,S,Cl)ࠢ Opal Hydrated Silica—SiOࠢ·_n_HࠢO Peridot (Mg,Fe)ࠢ(SiOࠤ) Quartz SiOࠢ Spinel MgAlࠢOࠤ Topaz AlࠢSiOࠤ(F,OH)ࠢ Tourmaline XYࠣAlࠦ(BOࠣ)ࠣ(SiࠦO₁ࠨ) (OHࠤ) [X is usually Na but may be replaced by Ca; Y is one of several metal ions] Turquoise CuAlࠦ(POࠤ)ࠤ(OH)ࠨ·4HࠢO Zircon ZrSiOࠤ Some ways to contact a local rock, mineral, or gem club If you have access to the most recent April Buyer’s Guide issue of the _Lapidary Journal_ magazine, scan its lists of gem and mineral clubs in the United States and other countries. (The address of the _Lapidary Journal_ is given in the list of journals cited below.) Talk to a member of the geology or earth science department of your local college or university. Talk to a member of the science department of your local high school. Write to the— Eastern Federation of Mineralogical and Lapidary Societies Box 10119 Alexandria, VA 22310-0119 or the Midwest Federation of Mineralogical and Geological Societies 306 Somonauk Park Forest, IL 60466 Check the phone book for your nearest rock and mineral shop and talk to the owners. Role of the U.S. Geological Survey (USGS) The USGS reports deposits that seem likely to contain gemstones. It is not a function of the USGS to exploit such resources. USGS geologists perform continuing research on kimberlites, the initial source of diamonds. Not all kimberlites are diamond-bearing, and some of the research is directed to learning what indications you look for during exploration to distinguish fertile from barren kimberlite. USGS geologists are compiling a U.S. map showing the locations of known kimberlites. Selected general references A trip to your local library is the best first step toward understanding gemstones and toward planning a trip to gem and rock shops or to places where you may be able to collect gemstones.