WHAT IS IT?

• An igneous rock of ultramafic composition (low silica) in the Peridotite group
  
  
• Greater than 90% Olivine, with other minerals, such as Pyroxene, Chromite, Magnetite, & Pyrope
  
  
• Olivine is an orthosilicate (contains (SiO₄)^4- anion)
  
  
• Typically contains an Mg/Fe ratio of 9:1
  
  
• Coarse grained
  
  
• Color:  light yellowish green to dull brown
  
  
• Soft, hardness of 3.5 to 4
  
  
• Dunite & other Peridotite minerals are the major constituents of the upper mantle of the earth
  
  
• Named after Dun Mountain near Nelson, New Zealand, where a deposit was discovered by the German geologist Ferdinand Con Hochstetter in 1859
  
  
• Also called Olivinite (not to be confused with Olevenite)
  
  
• Formed by:
  
  
  • Fractionation of Olivine from a mafic melt
    
    
  • Replacive formation by the reaction of pyroxene-bearing host rock with Olivine saturated magma dissolving the orthopyroxene in the host producing crystallized Olivine
    
    

COMPOSITION

• The composition of the main component, Olivine, is (Mg²⁺,Fe²⁺)₂SiO₄
  

• Typically contains an Mg/Fe ratio of 9:1
  
  

WHERE IS IT FOUND?

• Usually found in ophiolite (uplifted ocean crust with some mantle material attached)
  
  
• Commonly found with Platinum group metals, Chromite & Magnetite
  
  
• Rarely found within continental crust materials
  
  
• The largest deposits (by millions of tons) are:
  
  
  • Aaheim, Norway (2000 MT)
    
    
  • Twin Sisters Mountain, Washington State, near Mt Baker (1800 MT)
    
    
  • Arutats, Sweden (1800 MT)
    
    
  • Troodos Mountains, Cyprus
    
    
• The Dunite in the Bushveld Igneous Complex of South Africa contains large reserves of Platinum
  
  
• The Dunite dikes of the Fidalgo formation on Cypress Island (in the San Juan Islands) have had limited Chromite mining (200 tons)
  
  

WHAT IS IT USED FOR?

• Dimension stone for construction
  
  
• Cement manufacture
  
  
• Construction aggregate
  
  
• Polished countertops
  
  
• Fertilizer manufacture
  
  
• Carbon sequestration
  
  Mg₂SiO₄ (olivine) + 2CO₂ -> 2MgCO₃ (magnesite) + SiO₂ (silica)
  
  
• A mined source of Magnesium, Chromium, and Platinum
  
  

• Ornamental use - bowls, vases, desk sets, clock bases, carved animals, fruit, flowers, legendary figures, deities, busts, statues, etc.

• Metallurgy - Flux agent in blast furnaces