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What is a mineral?

What is a mineral?. A mineral is a (1) naturally occurring (2) inorganic , (3) solid with a (4) definite chemical composition and (5) crystalline structure . There are over 4000 known minerals, but only about 20 are common. What is a mineral? (cont.).

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What is a mineral?

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  1. What is a mineral? • A mineral is a (1)naturally occurring (2)inorganic, (3)solid with a (4)definite chemical composition and (5)crystalline structure. • There are over 4000 known minerals, but only about 20are common.

  2. What is a mineral? (cont.) • Minerals can either be a made of a pure substance – a single element (gold, silver, lead, iron) BUT Most minerals are compounds • The same elements are found in most minerals – they are called mineral forming elements: • Oxygen; Silicon; Aluminum; Iron; Calcium; Sodium; Potassium; Magnesium

  3. How do minerals form? Minerals can form several ways: • From molten rock/magma • Due to intense heat and pressure • Evaporation • Chemical Action

  4. What are silicates? • Minerals are classified into 2-groups based on their composition: • Silicate Minerals • Nonsilicate Minerals

  5. Silicate Minerals • Are minerals made of the 2 most abundant elements in Earth’s crust – silicon (Si) and oxygen (O) • A silicate may also contain one or more metallic elements like aluminum or iron • There are a few silicates that do not contain metals – like quartz • More that 90% of the minerals in Earth’s crust are silicates • Examples – feldspars, quartz, hornblende, olivine, muscovite, biotite

  6. Nonsilicate Minerals Groups • Carbonates – metal + C + O • Halides – metal + halogen • Native elements – single element • Oxides – Metal + O • Sulfates – S + metal + O • Sulfides – S + metal

  7. How To Identify Minerals Based on Properties

  8. quartz Color selenium calcite quartz

  9. Color • First thing noticed • Not useful property to identify minerals because: • One mineral can have different colors • Different minerals can have the same color • However some minerals do have a distinct color. Examples: sulfur, malachite, cinnabar.

  10. Crystal Shape • Arrangement of its component atoms and/or ions • Responsible for the outward shape of the crystal • Crystal system affects a number of other properties such as cleavage, density, and hardness

  11. Luster • The way light reflects off the surface of a mineral • How you would tell someone how a mineral looks • Nothing to do with color or shape • Terms used are generally not scientific, but are meant to be descriptive

  12. Hardness • A good physical property in mineral identification • Measure of the strength of the structure of the mineral relative to the strength of its chemical bonds --- Stronger bonds = greater hardness • Hardness can be tested through scratching • A mineral can only be scratched by a harder substance

  13. Streak • Color of the powder of a mineral • To test for streak, rub a mineral across a tile of white unglazed porcelain and examine the color of the "streak" left behind • Two minerals that have similar outward color may have different colors when powdered. galena hematite

  14. Cleavage • Cleavage is a smooth break producing what appears to be a flat crystal surface that can be broken along the same parallel plane over and over again • Terms are: perfect, imperfect, good, distinct, indistinct, and poor. biotite

  15. Fracture • Fracture is a description of the way a mineral tends to break • The surface that can be described as Smooth, Irregular, Jagged, Splintery • Most common fracture type is conchoidal which is a smoothly curved fracture that looks like broken glass

  16. Specific Gravity • Compares the density of a mineral to the density of water • If a mineral has a SG of 2, then it is twice as dense as water • If a mineral has a SG of 3 then it is three times as dense as water and so forth.

  17. Additional Mineral Properties

  18. Acid Test • Carbonate minerals (calcite & dolomite) tend to react to acids • The reaction is written as follows for calcite, the mineral for which this test is made famous: CaCO3 + 2H(+1) -------> Ca(+2) + H2O + CO2 (gas)

  19. The Fluorescence Minerals • Light from these ultraviolet lamps reacts with the chemicals of a mineral and causes the mineral to glow; this is called fluorescence. • Examples: • Fluorite • Calcite • Autunite • Willimite

  20. Magnetism • Magnetite is a natural magnet, which is a good way to identify it from other metallic mineral ores.

  21. Taste • Most commonly "tasted" mineral is halite/rock salt • YOU should never do this because there are minerals that are poisonous • Some solubility in water is required in order to have a taste

  22. The Scent of a Mineral • The most renowned smelly mineral is sulfur • Marcasite gives off a noticeable sulfur-like odor when it decomposes • Arsenic minerals tend to have a garlic scent as is consistent with the element and poison arsenic • Clay minerals have a clay-like smell that is sometimes called earthy

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