1. 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

2. Some Silicate structures Single tetrahedrons, single chains, double chains, sheets, rings, and 3-D networks

4. SINGLE SILICATE TETRAHEDRA Garnet (red) Olivine (green) (Fe,Mg)SiO 4 crystal

5. SINGLE CHAIN SILICATES Pyroxene Group [Fe,Mg,Ca,Al silicates]: –Augite (note the near 90 o angle of the two cleavages)

6. DOUBLE CHAIN SILICATES Amphibole Group [Na,Ca,Fe,Mg,Al silicates w/ H 2 O]: –The mineral hornblende is common –Nnote the 156 degree angle of the two cleavages

7. SHEET SILICATES Muscovite mica [K,Al + H 2 O] Biotite mica [K,Mg,Fe,Al + H 2 O] –Note the single perfect cleavage and elastic sheets TalcKaolinite (clay) [K,Al + H 2 O]

8. ZEOLITE RING SILICATES Naturalite from North Mountain Basalt Formation

9. FRAMEWORK SILICATES Feldspar group: –Most abundant mineral group –Orthoclase (K-feldspar) –Albite (Na-Plagioclase) –Labradorite (Ca-rich Plagioclase) 2 cleavages note twinning lines

10. FRAMEWORK SILICATES Quartz (SiO 2 ), the most common mineral: Chalcedony (SiO 2 ): –microcrystalline quartz –many var. (chert, jasper, flint) amethyst quartz crystal milky quartz rose quartz

11. FRAMEWORK SILICATES Hexagonal quartz crystal

12. FRAMEWORK SILICATES Amethyst (quartz) geode from the Scots Bay Formation

13. FRAMEWORK SILICATES Amethyst (quartz) geode replacing small straight tree trunk surrounded by chert ( from Scots Bay Fm)