Rocks are usually combinations of two or more minerals. The portions of different minerals making up rocks may vary, and the combinations of minerals may change within rocks of the same name. Granite, composed of quartz and potassium feldspar - usually with small amounts of mica or hornblende, may contain as many as a dozen other minerals. In addition, the portions of each of the minerals may shift from one deposit to another. This gives rise to the variety of local names.

Because rocks are made up of varying mixtures of minerals, and because there are about two thousand different minerals, the number of possible combinations is limitless. It is therefore very difficult to classify rocks except in broad, general groups. The most general classification of rocks is by method of formation: Igneous, Sedimentary and Metamorphic.

Mineral specimens are normally examples of a specific mineral or assemblage of minerals collected by people. Mineral specimens can also include rock types. Examples of mineral specimens found in Arizona include: quartz, azurite, malachite, selenite and calcite. A few of these found on BLM public lands in Arizona are:

Quartz Crystals; Phoenix, Yuma

Selenite; Arizona Strip

Semi-precious gemstones are used in jewelry-making and decorative arts. They are usually rocks that can be faceted or polished and are able to hold a shine. To collect semi-precious gemstones for commercial purposes, or in amounts greater than those indicated in this pamphlet, you should locate a mining claim. Contact your local BLM office to obtain information on locating a mining claim.

Examples of semi-precious gemstones found in Arizona are agates, fire agates, jasper, onyx and Apache tears. A few of these found on BLM public lands in Arizona are:

Fire Agate; Kingman, Safford

Apache Tears; Kingman, Phoenix

Petrified wood can be found in Arizona within the jurisdiction of the BLM Phoenix, Safford, Yuma and Arizona Strip Field Offices.

Collecting of mineral and fossil resources in prohibited in certain areas being managed under special designation to protect their scientific and natural values, such as Research Natural Areas.

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