Minerals An Introduction

Minerals: what are they? A mineral is a naturally occurring, inorganic solid with an orderly crystalline structure and a definite chemical composition. Yes, this means that coal is not a mineral.

How minerals form Crystallization from magma: crystals form as the temperature drops below their melting points; iron, calcium, magnesium minerals solidify first, sodium, potassium, and aluminum at lower MP. Examples: Feldspar (used for ceramics) Quartz (used for glass manufacture) Muscovite (common white Mica) Hornblende

How minerals form Precipitation: minerals are dissolved in water Common minerals: Halite (NaCl), which we know as salt Gypsum (CaSO4·2H2O) Calcite (CaCO3)

How minerals form Pressure and temperature: some minerals form when preexisting minerals/rocks are subjected to high temperatures and pressures. Examples: Garnets in schist Chlorite

How minerals form Hydrothermal solutions: high temperature solutions (100-300C) flowing through existing minerals/rocks, dissolve and reform into new minerals. Examples: Quartz (SiO2) Pyrite (FeS2)

Mineral Groups There are over 3800 named, indentified minerals, and they are broken into groups; here are some of them: Silicates: minerals with a framework of silicon and oxygen; they are the most numerous group. Carbonates: very common; usually a salt of a metal and the carbonate ion: CO3-2. Oxides: usually metals that have reacted with oxygen Sulfates and sulfides: metals that reacted with sulfur, some further reacted with oxygen/water/solutions Halides: minerals where metals have reacted with halogens (group 7A) Native elements: some elements that are found without having reacted with another element: Gold, Silver, Copper, Sulfur, Carbon (diamond, graphite)

Mineral Properties Each mineral has its own unique set of characteristics. Color Streak: color in a powdered form or when rubbed against an unglazed white tile Luster: reflection/sheen Crystal form: showing the internal crystal lattice in an external form Hardness: a relative scale: Mohs Cleavage: tendency to break along flat surfaces Fracture: when mineral do not cleave, the type of broken surface that does occur. Density/specific gravity: ratio of a mineral/substance’s mass to its volume. Others: feel (talc: greasy)