Using Characteristics of Minerals to Identify Them. Most minerals can be characterized and classified by their unique physical properties: hardness, luster, color, streak, specific gravity, cleavage, fracture, and tenacity.
The physical properties of minerals are determined by the atomic structure and crystal chemistry of the minerals. The most common physical properties are crystal form, color, hardness, cleavage, and specific gravity. One of the best ways to identify a mineral is by examining its crystal form (external shape).
Here are some suggestions:
Look for glossy black or dark green crystals and cleavage fragments forming flattened prisms in cross-section (corner angles of 56 and 124 degrees). Crystals may be short or long, and even needle-like in amphibolite schists. Characteristics: Glassy luster; hardness of 5 to 6.
The most reliable way to identify a mineral using color is the streak test. It is more reliable because even though the color of a specimen can vary its streak is usually the same.
The physical properties of minerals are related to their chemical composition and bonding. Some characteristics, such as a mineral's hardness, are more useful for mineral identification. Color is readily observable and certainly obvious, but it is usually less reliable than other physical properties.
Geologists use the following tests to distinguish minerals and the rocks they make: hardness, color, streak, luster, cleavage and chemical reaction. A scratch test developed by a German mineralogist Fredriech Mohs in 1822 is used to determine mineral hardness.
The most common rock-forming minerals are silicates (see Vol. IVA: Mineral Classes: Silicates), but they also include oxides, hydroxides, sulfides, sulfates, carbonates, phosphates, and halides (see Vol. IVA: Mineral Classes: Nonsilicates).
Mineral Identification Tools
If part of a crystal breaks due to stress and the broken piece retains a smooth plane or crystal shape, the mineral has cleavage. A mineral that never produces any crystallized fragments when broken off has no cleavage.
Mica is one of the easiest to identify of all minerals because it occurs in flat sheets, like fused-together sheets of cellophane or glass. Often thin sheets of mica are easy to separate from one another -- they easily exfoliate.
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