Minerals That compose the Earth’s Crust

What is a mineral? Is it inorganic? Nothing alive or alive at one time qualifies. Does it occur naturally? Nothing human- made qualifies. Is it a crystalline solid? If there are no crystals it does not qualify. Does it have a consistent chemical composition? Same ratio of compounds through out.

Kinds of Minerals Silicate Minerals - all silicate minerals contain some combination of Si (silicon) and O (oxygen). Make up 96% of Earth’s crust. Non-silicate Minerals – as indicated by the name, they contain no silicon and fall into 1 of 6 classes of non-silicates. Only 4% of Earth’s crust is made of non-silicates. – Carbonates - compounds that contain a carbonate group (CO3)

Non-silicates continued – Halides - compounds that consist of chlorine or fluorine combined with sodium, potassium, or calcium. – Native elements - elements such as gold, silver, and copper. – Oxides – compounds that contain oxygen and another element other than silicon. – Sulfates – compounds that contain a sulfate group (SO4). – Sulfides - compounds that consist of 1 or more elements combined with sulfur.

Crystalline Structure Crystal - a solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern. – Silicate minerals – all silicates will have a silicon- oxygen tetrahedron. These tetrahedron combine in different arrangements to form different silicate minerals. – Non-silicate minerals - since non-silicates have such diverse chemical combinations, there are a vast variety of non-silicate crystals.

Identifying Minerals The physical properties of minerals are helpful in identifying them. – Color - is the least helpful because some minerals can be seen in a variety of colors. – Streak - is the powdered form of a mineral. Usually created by rubbing the mineral on a streak plate. – Luster - how light is reflected by the mineral. Usually described as metallic or non-metallic.

Identifying Minerals continued – Cleavage and Fracture – cleavage is the tendency for some minerals to split at joints. Fracture is the tendency of other minerals to break unevenly. – Hardness - the ability of a mineral to resist scratching or the ability to scratch other materials. This is based on the Mohs Hardness Scale. – Crystal shape - there are 6 basic crystal shapes and this influences what type of a mineral it can be. – Density - is also a key identifier for minerals, based on the ratio of mass to volume.

Identifying Minerals continued Special Properties of Minerals - some minerals have other properties that aid in identifying them. – Fluorescence and Phosphorescence – fluorescence is the ability of a mineral to glow when in the presence of a U-V light and phosphorescence is the ability for the mineral to continue to glow after the U-V light has been turned off. – Chatoyancy and Asterism – chatoyancy is the ability of a mineral to display a silky appearance when reflecting light and asterism is displaying a six-sided star when reflecting light.

Special Properties continued – Double refraction - the ability to bend light as it passes through the mineral to show a double image of what is behind the mineral. – Magnetism - some minerals will have magnetic abilities. – Radioactivity - some minerals are radioactive, meaning the nuclei of the atoms are unstable and break down over time. This special property is detectable with a Geiger counter.