Introduction to Mineralogy-1_Scope, definition of Minerals and Mineraloids

Scope and aim of Mineralogy
Mineralogy is the study of minerals.
A geologist considers minerals as the basic building blocks comprising nearly the entire crust of the Earth.
If geologists are to understand the Earth, its formation, and its dynamics, they must understand minerals.
The beginning of this particular branch of science extends well back to prehistoric times.
Evidence of mining and smelting minerals to extract useful metals such as copper, lead, and zinc is found in many ancient civilizations shows that our ancestors surely knew about and used many minerals.
Almost every human endeavor is influenced by minerals.
Knowledge of minerals is essential in many engineering fields.
Miners and gem dealers view minerals as commodities to process and sell, while industrial manufacturers see minerals as the raw materials for marketable products.
In the electronics industries, minerals or their synthetic equivalents are used to make computer chips, diodes, capacitors, superconductors, and other crucial components.
The chemical composition, structure, and texture of the minerals that comprise the rocks provide evidences that guide geoscientists to decipher the history of the earth.
Define Minerals
Minerals are chemical compounds that are normally crystalline and form by geological processes. They must also have a well-defined chemical composition.
Crystalline: “having an orderly and repetitive atomic structure,”
The atoms and/or ions that comprise crystalline materials are arranged and chemically bonded in a regular and repeating long-range pattern.
Well defined: “varying within limits.”
Naturally occurring: formed without the benefit of human action or intervention.
Defn: Mineral is a naturally occurring crystalline solid with a definite, but not necessarily fixed, chemical composition.
Many crystalline solids with the same chemical and physical properties as their natural mineral counterparts may be synthesized in the laboratory. These materials are synthetic minerals.
Solids such as glass lacking long-range atomic order are considered amorphous. They are not minerals.
To be considered crystalline a material must be a solid, though, it may deform in a ductile manner under high temperature-pressure conditions.
Organic/ In-organic: In the past, a substance was not considered a mineral if it was the result of an organic process.
Biogenic crystalline substances such as calcium phosphate (apatite) in bones or teeth, or calcium carbonate (calcite or aragonite (CaC03)) in shells, to be minerals. These shells are a major component of many limestone layers.
The pyrite (FeS2) found in many shale and coal beds is produced by the action of sulfate reducing bacteria.
All minerals have a definite chemical composition; a chemical formula may be written for any mineral.
An example is the common mineral quartz (Si02), which is composed of silicon and oxygen in a ratio of 1:2.
The composition of many mineral species may vary within certain limits.
An example is the mineral olivine, which may be iron rich (Fe2Si04) or magnesium rich (Mg2Si04), or may have an intermediate composition. However, the proportions always work out so that the ratio (Fe + Mg):Si:O remains 2:1:4.
Hence, different samples of a mineral species may have different compositions, but the variability is limited.
Synthetic diamonds and rubies, for example, are not considered true minerals because they are not natural.
Ice is a mineral, but its liquid counterpart, water, is not.
Refined sugar is crystalline but is not considered a mineral because it is human made.
Window glass, made mostly from quartz, is not a mineral because it is not crystalline.
Define Mineraloids
Mineraloids are mineral-like materials that lack a long range crystalline structure. They include amorphous solids and glasses.
Amorphous solids lack long-range atomic order, but may posses short-range (-10-100 Å) order.
E.g., Opal, which consists of silica gel, often arranged in small spherical masses.
The crystalline structure of U- and Th- bearing minerals such as zircon may be extensively disrupted by radioactive bombardment. The term metamict is applied to these disrupted structures, and once a mineral's structure becomes metamict, it is properly considered a mineraloid.
Natural glasses may also be considered mineraloids. E.g., Volcanic glass.
Meteorite impacts may release enough energy to melt the rocks that they strike.
A lightning strike may heat soil or rock sufficiently to melt some of it and produce a fulgarite.
Burning coal beds may generate enough heat to fuse the surrounding rock forming scoriaceous or slag-like glasses referred to as ash glass or clinker.