Rocks and Minerals
AND they have
From the earliest time to the 16th century the interest in minerals was primarily economic. The science of mineralogy arose in central European mining districts
Mineral Classification
The purpose of classification is to group similar objects and distinguish between dissimilar objects. The earliest classifications were based on the uses of minerals as ores or for their mystical and medicinal properties.
One of earliest classifications based on physical properties was proposed by Agricola (George Bauer) (1494-1555). His main contribution was in the description of new minerals, their mode of occurrence and mutual relations (paragenesis).
Steno (Niels Stensen) (1669) formulated and Rome de l'Isle (1772-1783) confirmed the law of the constancy of interfacial angles:
For all crystals of the same substance the angles between corresponding faces have a constant value
Rene Just Hauy (1743-1821) developed a model to explain the constancy of mineral forms. This model states that mineral forms are due to on stacking of basic structural 'units'. We now know the 'units' are fundamental atomic and molecular arrangements
In the last quarter of the 18th century - Chemical methods of classification first appear. In 1800 start getting approximately accurate chemical analyses. A.G. Werner (1749-1817) emphasized the usefulness of chemical classification and the need for good descriptions
Berzelius (early 19th century) was a leader among mineralogists who demonstrated the chemical constitution of minerals affords a basis for a satisfactory classification. He recognized the law of multiple proportions, which is expressed in the chemical formula. The chemical formula gives the kind and proportions of elements present.
The commonly used chemical classification is based on the kinds of elements in the mineral. To learn more about elements, you can consult a period table of the elements. There are several of these on the web which also give information about the properties of individual elements.
Periodic Table 1 - A very complete database about elements
Periodic Table 2 - A good basic reference to elements
- Minerals of one type of atom - native elements (Au - gold, Ag - silver, Cu - copper, among others).
- Minerals with cations combined with the large, negative ions (anions): oxygen (O - oxides), sulfur (S - sulfides), halogens (Cl, F or Br - halides) .
- and anions groups made of oxygen combined with cations of valency +3 or greater (see periodic table - non-metals of groups 13-17): silicates (SiO4), carbonates (CO3) and sulfates (SO4).
The physical properties used for mineral identification depend on the nature and arrangement of the constituent atoms
This arrangement, known as crystal structure is determined by:
How are mineral's formed in nature?
From a water solution. The chemicals in the solution come from dissolving other minerals. These minerals form
From a silicate melt. The melt comes from melting minerals. These minerals form
- Where molten rock cools - either in the interior or at the surface (igneous).
By adding energy to minerals, rearrange the ions of the old structure and make a new one. These minerals form
- Inside the earth where high temperatures provide the necessary energy (metamorphic).