G 101    Lectures     Sample Test

Minerals

Minerals

• naturally occurring

• inorganic

• solid

• fixed composition or within fixed range
   

Physical properties:

• Hardness
  Mohs scale

• Luster

• Color : unreliable (quartz: smoky, milky, purple, red, clear, etc.)

• Cleavage

• Fracture : conchoidal (quartz); fibers (asbestos group)

• Specific Gravity

• Special properties:

  • Feel

  • Taste : halite

  • Smell : sulfur  and sulfides

  • Magnetism – magnetite

  • Fizz in dilute HCl acid : calcite

Mineral Groups

Silicates

Silicon-Oxygen tetrahedron
About 600 known, make up 95 % of lithosphere and upper mantle
Classification based on Si – O arrangement:

• Framework silicates, most abundant:
  Quartz
  Feldspars:
      Orthoclase, K-rich
      Plagioclase, Na, Ca-rich
  

• Sheet silicates:
  Micas:
      Al-rich, light - Muscovite
      Fe-rich, dark - Biotite
  

• Chain silicates:
  Single chain - Pyroxenes
  Double chain - Amphiboles
  

• Single tetrahedron:
  Olivine

Nonsilicates

• Oxides : compounds made of oxygen and metal or other ions
  Hematite
  Magnetite
  Corundum
  

• Carbonates: most common after silicates; basic unit carbonate ion (CO₃)^-2 combined with Ca, Mg, Fe, Cu, etc. Among about 80 known carbonates the most common are
  Calcite
  Aragonite
  Dolomite
  

• Sulfides: combinations of one or more metals with sulfur
  Galena
  Pyrite
  

• Sulfates: basic unit sulfate ion (SO₄)^-2 combined with Ca, Mg, Fe, Cu, etc.
  Gypsum (Selenite, Satin Spar, and Desert Rose)
  Anhydrite
  

• Native elements: about 20 of them, often occur in pure form
  Metals:
  Gold
  Silver
  Platinum
  Nonmetals:
  Diamond
  Graphite
  Sulfur
  

Gems

Gem Minerals

• Diamond
  Diamond forms at great depths within the lithosphere, where pressures are in excess of 200 kilobars and temperatures of 800° C or higher. Due to its hardness and resistance to acids ancient Greeks called it adamas meaning “the invincible”. The rock in which diamonds occur is kimberlite (metamorphosed pegmatite) found in areas of Siberia, South Africa, India, Zaire, Australia, etc. Most commonly diamonds are found in alluvial deposits, but also mined directly from kimberlite (diamond pipes). Less than 25 % of total world’s production of diamonds is suitable for gems. The value of diamonds depends on the four “C’s”: color, clarity, cut, and carat weight. The most valuable are colorless and blue-white stones. The world’s largest diamond is Cullinan, found in South Africa in 1905. Cullinan weighs 3106 carats (1 carat = 0.2 grams). First diamonds were synthesized in 1955 in the United States.
  
• Emerald
  Emerald is green color variety of silicate mineral beryl. Most commonly it occurs in igneous rocks (pegmatite and granite) but also in metamorphic rocks (mica schists). The most valuable emeralds are found in Colombia. Other areas of significant emerald production are South Africa, Zimbabwe, and Russia. Emerald is often considered more valuable than diamond.
  
• Ruby
  Ruby is red color variety of oxide mineral corundum. It occurs in metamorphic rocks (marble, gneiss, mica schist) but also in silica deficient igneous rocks such as siyenites. Name of the gem was derived from Latin ruber, meaning red. The most valuable rubies have deep red color, known as a pigeon-blood, and seldom are larger than three carats. The finest Mogok rubies come from Myanmar (Burma). Other areas include Tailand, Cambodia, Sri Lanka, Kenya, etc.
  
• Sapphire
  From Latin sapphirus, meaning blue; blue variety of corundum. Sapphires are much more abundant, thus less valuable than rubies. Some of the largest samples exceed 100 carats. The most highly prized are cornflower-blue stones from Cambodia found in alluvial deposits. Other areas of significant production are Tailand, Sri Lanka, India, and Australia.
  
  Semiprecious gems:
  
• Pearl
  One of the oldest known gems. Certain species of saltwater oysters and freshwater clams build concentric layers of aragonite around sand that penetrates their epithelum (mantle). Pearls may grow flat (blister pearls), irregular (baroque pearls), but most valuable are spherical or drop like pearls. The color of pearls varies with the mollusk species and water environment. The most valuable are rose Indian pearls. Other colors are cream (Persian Gulf and Japan), white with greenish and bluish shades (Australia), black and reddish-brown (Mexico), golden-brown (Panama) etc. The value of natural pearls significantly decreased after huge quantities of cultivated pearls invaded the world market.
  
• Amber
  Amber is a hardened resin of coniferous trees, usually yellowish brown, but occasionally deep brown to red, green, or blue. Trapped insects, air bubbles, and dust particles may be found in some specimens. The most abundant amber particles are found along the shores of the Baltic Sea, along the coast of Sicily, and Myanmar (Burma).
  
• Coral
  Marine organisms that live in large colonies in shallow, warm, and clear seas. Their skeletal parts precipitate as aragonite and calcite in many different colors and shapes. The most sought are branch-like corals in red, reddish-rose colors (Mediterranean off the coast of Algeria) and black horn-like corals (Hawaii).

G 101     Lectures     Sample Test