Minerals

A mineral is a naturally occuring, inorganic, crystalline solid with a specific chemical composition. NATURAL Minerals are created by the Earth itself…not from human influence. INORGANIC Minerals are not made by living things or are composed of living things. CRYSTALLINE The arrangement of atoms within a mineral creates a crystalline structure. Each mineral has its own unique structure. CHEMICAL COMPOSITION Minerals are composed of one element or many elements in the form of a compound.

Chemical Composition of Minerals Some minerals are composed of a single element. Ex: Sulfur = S Some minerals are composed of a combination of elements known as a compound. Ex: Fluorite = CaF 2 (combination of calcium and fluorine) RT = Pg. 16

Crystalline Structure of Minerals The atoms with a mineral are arranged and bonded in a specific way creating the crystalline structure of the mineral. The crystalline structure of a mineral helps to determine that mineral’s physical and chemical properties – such as hardness and cleavage. The majority of the Earth’s crust (by mass and volume) is made up of the elements oxygen and silicon. The “silicon-oxygen tetrahedron” is the basic building block of many minerals. The arrangement of silicon-oxygen tetrahedrons determines the crystalline structure of minerals.

Rock vs. Mineral A rock is a naturally formed solid that is part of the Earth. All minerals are rocks, but not all rocks are minerals. Most rocks are composed of one or more minerals. Some rocks are composed of glassy or organic materials COAL Coal is composed of the organic remains of ancient plant and animal matter (organic). Minerals are inorganic. OBSIDIAN Obsidian is volcanic glass that is formed by heated rock being cooled very quickly. Glass has a noncrystalline atomic structure. Minerals have a crystalline structure.

Mineral Properties and Identification The best method for mineral identification is through the use of X- ray diffraction. A beam of X-rays passing through a mineral sample will diffract leaving a unique “x-ray pattern” on photographic film. Each mineral has its own unique diffraction pattern. Minerals have a unique set of physical and chemical properties that reflect its internal arrangement of atoms. When in the field, scientist will use other methods to identify minerals.

Mineral Properties and Identification Color The color of a mineral can be used for identification in some cases. Many times minerals will change due to impurities found within the rock or mineral. Color is NOT a reliable mineral property used in identification SULFUR Sulfur is well known for its yellow color. QUARTZ All three samples are of the same mineral. In this case color would not be useful tool in mineral identification.

Mineral Properties and Identification Streak The residue of a mineral left on a scratch plate is known as streak. The streak color does not always match the color of the mineral. The streak of a mineral is more consistent than the color of a mineral and, therefore, is a more reliable test for mineral identification. HEMATITE Hematite is a silver colored mineral. When scratched on a porcelain plate, its streak is reddish-brown.

Mineral Properties and Identification Luster The shine from an unweathered mineral in light is known as luster. Minerals may have metallic or nonmetallic lusters. A mineral with a metallic luster shines like a metallic surface (Ex: clean steel pot). Most minerals have a nonmetallic luster. PYRITE Pyrite has a metallic luster and shines like a metallic surface in the light. OLIVINE Olivine does not shine like a metallic surface in the light. It has a nonmetallic luster.

Mineral Properties and Identification Hardness The resistance to being scratched is known as a mineral’s hardness. Moh’s Hardness Scale is a tool used by scientists to determine the hardness of a mineral. Scientists can determine whether an unknown mineral can “scratch” or be “scratched” by known common materials. This will help a scientist determine the hardness of an unknown mineral. Gypsum has a hardness of 2 and calcite has a harness of 3. A fingernail has a hardness of 2.5. A fingernail can “scratch” gypsum and “be scratched” by calcite.

Mineral Properties and Identification Cleavage The tendency of a mineral to break along a zone of weakness is known as cleavage. Zones of weakness found within a mineral relate to the crystalline structure of the mineral. Sometimes zones of weakness can be seen as smooth sides with a luster. Minerals that lack zones of weakness will break or “cleave” along uneven surfaces. This is known as fracture. MUSCOVITE MICA GALENA CLEAVAGE: Zones of weakness FRACTURE: Uneven brake

Mineral Properties and Identification Other Tools for Mineral Identification Specific Gravity Specific gravity is the density of a mineral compared to that of water. Crystal Shape The geometric shape a mineral takes is known as crystal shape. Reaction with HCl acid Certain minerals will react in the presence of hydrochloric acid.