|
What is a mineral?
Minerals are the basic building blocks of the lithosphere. The rocks that we see around us are made up of one or more types of minerals. For example, granite often contains Quartz, Feldspar and Biotite; Basalt is mainly made up of Olivine, Pyroxene and Feldspar.
Minerals generally refer to naturally-occurring homogenous solids with a certain chemical composition and atomic arranged formed through inorganic action. Only those that meet these criteria can be considered a mineral. Artificial gem stones, stones found inside the body or pearls and ivory produced through biological processes are all not considered to be minerals.
Mineral Types
Constant study and research by Mankind has led to the discovery of new minerals. There are now more than 4300 types of named minerals in the world. Advances in the sensitivity and accuracy of analytical instruments have allowed new tiny minerals to be discovered in recent years.
Despite the small size of Taiwan and relatively youthful geological age, igneous, sedimentary and metamorphic rocks can all be found throughout the island and more than 200 types of minerals have been identified so far.
Mineral Classification
There are many ways to classify minerals but the most widely used method today is by chemical composition and crystal structure.
The system divides minerals into Class, (sub-class), Group (sub-group) and Species (sub-species).
（1） Class: Minerals with the same anion. Generally minerals are divided into fifteen major classes:
|
Number
|
Class
|
Specimen Mineral and Chemical Composition
|
|
1
|
Native Elements
|
Native Gold
|
Au
|
|
2
|
Sulphides and Sulfosalts
|
Pyrite
|
FeS2
|
|
3
|
Halides
|
Halite
|
NaCl
|
|
4
|
Oxides and Hydroxides
|
Magnetite
|
Fe3O4
|
|
5
|
Nitrates
|
硝石
|
KNO3
|
|
6
|
Carb
nates
|
Calcite
|
CaCO3
|
|
7
|
Borates
|
Borax
|
Na2B4O7·10H2O
|
|
8
|
Sulphates
|
Gypsum
|
CaSO4·2H2O
|
|
9
|
Chromates
|
Crocoite
|
PbCrO4
|
|
10
|
Tungstates
|
Scheelite
|
CaWO4
|
|
11
|
Molybdates
|
Wulfenite
|
PbMoO4
|
|
12
|
Phosphate
|
Apatite
|
Ca5(F,Cl,OH) (PO4)3
|
|
13
|
Arsenates
|
Erythrite
|
Co3(AsO4)2·8H2O
|
|
14
|
Vanadates
|
Vanadinite
|
Pb5Cl(VO4)3
|
|
15
|
Silicates
|
Natrolite
|
Na2Al2 Si3 O10‧2H2O
|
（2） Sub-class: Some mineral classes may have differences in the structure of the anion group so these are broken down into sub-classes. The very large Silicate class for example can be divided into six sub-classes:
|
Sub-class
|
Representative Mineral
|
|
Neosilicates
|
Olivine
|
|
Sorosilicates
|
Hemimorphite
|
|
Cyclosilicates
|
Beryl
|
|
Inosilicates
|
Diopside
|
|
Phyllosilicates
|
Muscovite
|
|
Tectosilicates
|
Quartz
|
（3） Group: Within a class or sub-class, minerals with similar chemical composition and the same crystalline structure are placed in the same group. Examples include the Feldspar group in the Tectosilicates sub-class or the Pyroxene group and Amphibole group in the Inosilicates sub-class.
（4） Sub-group: If there are two many minerals in a particular group, the cation type and crystal system of the minerals used to define sub-groups. The Feldspar group for example is divided into the two sub-groups of Plagioclase and Alkali feldspar.
（5） Species: Within a family or sub-family, minerals with the same chemical composition and crystalline structure are defined as belonging to the same mineral species, an example being Albite.
（6） Sub-species: Within a mineral species, if physical properties or differences in the amount of trace elements lead to significant differences then sub-species can be defined. Amethyst, Smoky Quartz, Citrine and Rose Quartz are all sub-species of Quartz for example. Sub-species of Beryl include Emerald, Aquamarine, Pezzottaite, Heliodor, Red Beryl and Goshenite.
National Museum of Natural Science
|
A Slice of Wonder
