Day 1
A
mineral is a naturally occurring, inorganic material with a fixed composition
and a repeating internal structure.
- a material which occurs only through artificial synthesis
is not a mineral
- the term 'inorganic' excludes hydrocarbons and other
molecules that can have crystalline (repeating and ordered) structures;
note that minerals can form through organic processes (e.g., apatite,
calcite, graphite, and pyrite are each minerals that can be precipitated
during the life activities of certain organisms).
- fixed composition means that we can write out a mineral
formula (e.g., calcite, CaCO3); mineral
compositions can vary within specified limits through substitutions (e.g.,
magnesium can substitute for calcium in calcite, and we can express that
as [Ca,Mg]CO3).
- repeating, or periodic, structure means there is a simple,
fundamental arrangement of atoms in a mineral, and this arrangement repeats
to form the mineral. In this sense, 'repeating internal structure' is synonymous
with the term 'crystalline'.
In addition to the many obvious minerals that you are
already familiar with, such as quartz, garnet, and diamond, consider the
following - are they minerals?
- Snow
- Mercury (room temperature)
- Mercury (absolute zero)
- Coal
- Crystals of acetic acid
- Calcite in a mollusc shell
- Obsidian
- Amber