Physical properties used for identifying a mineral
This site has a separate page for each of the most useful physical properties for identifying a mineral. Although some of these properties can be measured precisely (e.g. specific gravity), they are more commonly used qualitatively to identify minerals in the field, where no sophisticated equipment is available.
It is important to realise that while some properties are useful for identifying certain minerals, they may not be as useful for identifying others. Additionally, as no two specimens of a mineral form under exactly the same physical conditions, there can be a considerable variation in appearance (e.g. colour, crystal habit / mode of occurence) between two specimens of the same mineral found at different localities. Our photographs of calcite, fluorite, garnet and gypsum show how many visible variations there can be of the same mineral.
Variations of gypsum (rosette, rhombs and crystal)
Additionally, it is often useful to group the rock forming minerals into two main groups, based on their chemical composition. This can generally be done based on their colour.
Mafic minerals - These are minerals which are rich in Fe (iron) and Mg (magnesium). Mafic minerals are generally dark in colour - usually green, brown or black. The derivation of the term is ma for magnesium and fic for iron (from ferric).
Felsic minerals - These are minerals which are Si (silicon) rich, and most also have abundant Al (aluminium), Na (sodium) and K (potassium). Felsic minerals are typically light in colour and may be transparent or translucent. They are commonly white, light grey or pink. The derivation of the term is fel for feldspar and sic for silica.