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Elements Help (page 2)

— McGraw-Hill Professional
Updated on Sep 1, 2011

Sulfides

The minerals of the sulfide group are often made up of a metal combined with sulfur. They are recognized by their metallic luster. The s ulfides are an economically important group of minerals. The extraction of sulfide ores from composite metals is a standard process in industry. Specific ores are known for certain metal extractions, like cinnabar (a major source of mercury), molybdenite (molybdenum, an alloy in steel), pyrite (iron source), and galena (lead, used in piping and pewter).

Sulfates

The sulfate mineral group usually combines one or more metals with the sulfate compound, SO 4 . Most sulfates are transparent to translucent, light in color, and soft. They usually have low densities. Gypsum , the most plentiful sulfate, is found in evaporite deposits. Common sulfates include anhydrite (CaSO 4 ) and c elestine (SrSO 4 ).

Sometimes, sulfates contain substituted groups like chromate , molybdate , or tungstate in place of the sulfate group. Chromates are compounds in which metals combine with chromate (CrO 4 ). The minerals crocoite (PbCrO 4 ), wulfenite (PbMoO 4 ), and scheelite (CaWO 4 ) are all examples of different group replacements that form different minerals. These compounds are usually dense, brittle, and brightly colored.

Phosphates

The mineral group, known as the phosphates , is made up of one or more metals chemically combined with the phosphate compound (PO 4 ). The phosphates are sometimes grouped together with the arsenate , vanadate , tungstate , and molybdate minerals. These minerals have substituted arsenic, tungsten, and molybdenum elements, respectively.

Although geologists list several hundred different types of these minerals, they are not common. Apatite is the most common phosphate mineral. Most minerals in these groups are soft, but their hardnesses can range from Minerals and Gems Phosphates to 5 or 6 ( turquoise ). Although brittle, they have well-formed crystals in beautiful colors like lazulite (blue) and vanadinite (red or orange).

Carbonates

This is an easy one. Carbonates are minerals which contain one or more metals bonded with carbon in the compound (CO 4 ). Most pure carbonates are light colored and transparent. All carbonates are soft and brittle. They are usually found as well-formed rhombohedral crystals. Carbonates react with, bubble up, and dissolve easily in hydrochloric acid. Calcite is the most common carbonate. Other colorful carbonate minerals include rhodochrosite (pink to red), smithsonite (blue green), azurite (deep blue), and malachite (medium to dark green).

Nitrates and borates are often thought of as a subgroup of carbonates. They are formed when metal compounds combine with nitrogen and boron. When metals bond with nitrate, minerals like nitratine , a rare rhombohedral, transparent, often twinned mineral is formed.

When metals bond with borate, minerals like borax , kernite , and ulexite are formed. Most people have seen white borax, but it can also be colorless, gray, greenish, or bluish. Borax forms near hot springs, in ancient inland lakes, and places from which water has evaporated.

Organic Minerals

Minerals originally from organic sources (plants) are not usually classified as true (pure) minerals. However, some crystalline organic substances look and act like true minerals. These substances, formed primarily from carbon, are called organic minerals . Amber (petrified tree sap) is an example of an organic mineral.

Practice problems of this concept can be found at: Minerals and Gems Practice Problems

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