Chemistry of Minerals

Home Up

                                                           

 

     A mineral is a pure substance. It can be either an element or a compound. There are over 4,000 minerals known. They are made of the 92 natural elements found on the Earth. Crystals are sometimes called the "flowers" of the mineral kingdom. Fine crystals are relatively rare since there must be just the right conditions in the Earth for the crystal to grow. The specimens on this page are from my personal collection. What you see below is the natural crystal shape.  Only the Malachite specimen has been polished. The name, approximate size of the specimen, location and chemical composition is below the picture. All sizes are in centimeters. Click on the picture to see a larger view.

Im000810Quartz.jpg (45367 bytes) Im000811Calcite.jpg (44121 bytes) Im000814Galena.jpg (50738 bytes) Im000817Witherite.jpg (41847 bytes) Im000818Malachite.jpg (50379 bytes) Im000841Pyrite.jpg (42850 bytes)

Quartz SiO2 Mt. Ida, Arkansas 8.3 X 5.5 X 8.5

 Calcite CaCO3 Pitcher, OK  8 X 7.5 X 7.5 Galena PbS        Reynolds Co.,     MO. 6.1 X 9.2 Witherite on Fluorite BaCO3 Cave-in-Rock, So. IL 5.5 X 6.5 Malachite Cu2CO3(OH)2 Shaba Prov., Zaire 6 X 8 Pyrite FeS2 Logrono, Spain 3 X 3
Im000819Amazonite.jpg (46280 bytes) Im000820Quartz Sphalerite.jpg (38773 bytes) Im000840Apophyllite.jpg (42085 bytes) Im000839Celestite.jpg (46524 bytes) Im000838Crocoite.jpg (46446 bytes) Im000835Fluorite.jpg (47352 bytes)
Amazonite KAlSi3O8 Lake George, CO. 7 X 4.5 Quartz on Sphalerite SiO2  on ZnS 6.4 X 7.2  Apophyllite with    Stilbite KCa4Si8  O20(F,OH).8H2O Maharashtra, India 4.6 X 5.7 Celestite SrSO4 Rockwood, Michigan 4.6 X 6.6 Crocoite PbCrO4 Tasmania, Australia 4.6 X 6.5 Fluorite CaF2 Minerva Mine,So., Illinois 3.5 X 4.5

Dana Classification

This system has been in use by geologist for over 150 years. It is based on the chemical composition of the mineral. Below is a brief sketch of the scheme and a few examples of each division.

Native Elements- Elements that are found in their free uncombined state. Ex. Gold, Platinum, Silver and copper.

Sulfides, Arsenides and Tellurides- Compounds of some metal combined with sulfur, arsenic or tellurium. Ex. Galena (PbS), Chalcocite(Cu2S), Sphalerite (ZnS), Millerite (NiS) and Pyrite (FeS2)

Oxides- Compounds made from a metal plus oxygen. Ex. Cuprite (Cu2O), Hematite (Fe2O3), Cassiterite (SnO2), 

Halides- Compound consisting of a metal and a halogen (F2,Cl2,Br2 or I2). Ex. Halite (NaCl), Fluorite (CaF2)

Carbonates-The polyatomic ion CO3-2 combined with a metallic element. Ex. Calcite (CaCO3), Siderite (FeCO3), Smithsonite (ZnCO3), Witherite (BaCO3) and Dolomite (CaMg(CO3)2)

Sulfates- Compound consisting of a metal with the sulfate (SO4-2) ion. Ex. Barite (BaSO4), Celestite (SrSO4), Gypsum (CaSO4.H2O) and Epsomite (MgSO4.7H2O)

Chromates-Compounds consisting of a metal combined with the chromate ion (CrO4-2) Ex. Crocoite (PbCrO4)

Phosphates, Arsenates, and Vanadates- This group of minerals is made of a metallic element combined with the following ions: Phosphate (PO4-3), Arsenates (AsO4- ), Vanadates (VO4- ) Ex. Erythrite (Co3(AsO4)2.8H2O), Apatite (Ca5(PO4)3(F,Cl,OH), Mimetite (Pb5(AsO4)3Cl), Wavellite (Al3(PO4)2 (OH)3.5H2O)

Molybdates and Tungstates-Compounds of a metal and the molybdate ion (MoO4-2), or tungstate ion (WO4-2) Ex. Wulfenite (PbMoO4)

Silicates- Large group of minerals having silicon and oxygen in their formula. Ex. Quartz (SiO2), Opal (SiO2.nH2O), Danburite (CaB2Si2O8), Stilbite (NaCa2Al5Si13O36.16H2O) and many, many more.

Sources:

The Audubon Society Field Guide to North American Rocks and Minerals, Copyright 1978

Simon & Schuster's Guide to Rocks & Minerals, Copyright 1978