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Physical Geology Chapter 5 Big Definition! • Mineral – a natural, usually inorganic solid that shows – Characteristic chemical composition – Orderly internal structure – Recognizable physical properties Is it organic? Does it occur naturally? Is it a crystalline solid? Does it have a consistent chemical composition? Coal Brass Obsidian Basalt Fluorite No Yes Yes Yes Yes No Yes Yes Yes No Yes Yes No Yes Kinds of Minerals • Silicates – has some combination of silicon (Si) and oxygen (O) and comprise 96% of the earth’s crust • Non-silicates – no SiO compounds; 4% of the earth’s crust Silicate Minerals • Quartz – only Si and O • Feldspar – most common silicate • Ferromagnesians – iron and magnesium bearing compounds – olivine – Pyroxene – Amphibole – biotite Non-Silicate Minerals And Native Elements • All minerals in Earth’s crust have a crystalline structure of some kind. • That is its “regular orderly structure” What is a crystal? • A solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern • X-rays are used to study crystals • X-rays pass through a crystal and strike a photographic plate producing an image of the atom/molecule arrangement Diamond Silicate building block – the silicon/oxygen tetrahedron Silicate Mineral Arrangements • • • • • Isolated do not link to other O or Si Rings link by sharing O Single chains share O (open rings) Double chains are bonded single chains Sheets share 3 O with others; 4th with Al or Mg, which holds sheets • Frameworks bond each tetrahedron to 4 others; and on and on………….. Non-silicate arrangement • Vast variety of crystalline structures • May have tetrahedra similar to silicates but with different elements at center • Minerals with same ion at center share properties, thus creating subgroups How do we identify minerals? • By physical properties such as – Color – Streak – Luster – Cleavage and fracture – Hardness – Crystal shape – density • Or by special properties such as – Fluorescence – Phosphorescence – Chatoyancy – Asterism – Magnetism – Radioactivity – Double refraction Color • Many typical colors, but additions of elements can cause changes; e.g., • quartz vs. Amethyst Click here for more information Streak Click here for more information Luster • Click here for more information Cleavage and fracture • Click here for more information Hardness • Click here for more information Crystal shape • Click here for more information Specific gravity • Click here for more information Special properties • Click here for more information