Framework Silicates

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Framework Silicates

• Quartz and feldspar

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Framework?

• Normally called Tectosilicates
• Formal name
• Framwork of a large building,
• Si and O fit together

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Quartz (SiO2)

• Color?
• Crystal growth?
• Cleavage/fracture?
• Habit?
• Hardness?
• Luster?

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Microscope
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Feldspars

• The most common minerals on Earth
• Oxygen is due to its large size and enormous
  abundance makes up 94 of the Crust
• Silicates (6 Si) and Oxides make up the largest
  part of the minerals you will see

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Feldspars

• Classified by the triangle
• Albite (NaSi)
• Orthoclase (KAl)
• Anorthite (CaAl)
• About 20 Feldspars
• The nine to your right are the important ones at
  the earths crust (that your ever going to see)
• How do we tell the difference?
• Structure and Chemistry
• Breaks down into two groups

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FeldsparsAlkali Feldspar

• Why Alkali???
• Because they are Alkali element (Na, K)
• (K,Na)AlSi308 KAISi308 (orthoclase)
• Perthitic texture
• Right angle cleavage
• Ancient Greek (Orthoclase)
• the Greek orthos, straight or right, and klasis,
  a break or fracture.

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K-Feldspars

• Alkali Feldspars
• Orthoclase
• Sanidine
• Microcline
• Anorthoclase
• Also known as the K Feldspars

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Plagioclase Feldspar

• Plagioclase feldspars ( NaAISi308 to
  CaAl2Si308) Albite to Anorthite
• Albite Twinning
• Oblique angle cleavage
• Plagioclase takes its name from the Greek
  plagios, oblique, and klasis, a break or
  fracture.

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Plagioclase Feldspars (Potash)

• Albite
• Oligoclase
• (sun/moonstone?)
• Andesine
• Andesites
• Labradorite
• colorful across cleavage planes (labradorescence)
• Bytownite
• Rare
• Anorthite
• Pretty rare

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What to look for today(thin section)

• Plagioclase
• Albite twinning

• Alkali Feldspars
• Carlsbad twinning
• perthites

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Rarely viewed specimen

• Microcline
• Tartan
• Cross hatched