Silicon Tetrahedra by Charina Cameron
• 4 oxygen atoms
• 1 silicon atom in the center
• Forms a 4-sided geometry
• Each side is like an equilateral triangle
• Creates a 4- ion
Some Silicate structures• Single tetrahedrons, single chains, double chains,
sheets, rings, and 3-D networks
SINGLE SILICATE TETRAHEDRA
• Garnet (red)
• Olivine (green)(Fe,Mg)SiO4
crystal
SINGLE CHAIN SILICATES
• Pyroxene Group [Fe,Mg,Ca,Al silicates]:
– Augite (note the near 90o angle of the two cleavages)
DOUBLE CHAIN SILICATES
• Amphibole Group [Na,Ca,Fe,Mg,Al silicates w/ H2O]:
– The mineral hornblende is common– Nnote the 156 degree angle of the two cleavages
SHEET SILICATES
• Muscovite mica [K,Al + H2O] Biotite mica [K,Mg,Fe,Al + H2O]
– Note the single perfect cleavage and elastic sheets
• Talc Kaolinite (clay)
[K,Al + H2O]
ZEOLITE RING SILICATES
• Naturalite from North Mountain Basalt Formation
FRAMEWORK SILICATES• Feldspar group:
– Most abundant mineral group– Orthoclase (K-feldspar)
– Albite (Na-Plagioclase)
– Labradorite (Ca-rich Plagioclase)
2 cleavages
note twinning lines
FRAMEWORK SILICATES• Quartz (SiO2), the most common mineral:
• Chalcedony (SiO2):– microcrystalline quartz– many var. (chert, jasper, flint)
amethyst
quartz crystal
milky quartzrose quartz
FRAMEWORK SILICATES
• Hexagonal quartz crystal
FRAMEWORK SILICATES
• Amethyst (quartz) geode from the Scots Bay Formation
FRAMEWORK SILICATES
• Amethyst (quartz) geode replacing small straight tree trunk surrounded by chert (from Scots Bay Fm)