Isolated, double, and ring silicates

Question 1

Olivine

Answer 1

(Mg, Fe)₂SiO₄

• _{dull green, beige-green}
• _{lumpy (epidote is angular)}

Question 2

Garnet

Answer 2

(Mg, Fe, Mn, Ca)₃(Al, Fe, Cr)₂(SiO4)₃

• dodecahedron/trapezohedron crystal shape
• deep brownish red

Question 3

Zircon

Answer 3

ZrSiO₄

• tetragonal (dipyramid) crystals

Question 4

Aluminum Silicates

Polymorphs andalusite, kyanite,
sillimanite

Answer 4

Al₂SiO₅

Andalusite

• four point cross in cross section
• squarish shape in cross section

Kyanite

• blue blades
• different hardness in two directions, glass will scratch length wise but not in the cross section

Sillimanite

• kyanite w/o the blue, white blades

Question 5

Topaz

Answer 5

Al₂SiO₄(F, OH)₂

• looks like a gem
• orange

Question 6

Staurolite

Answer 6

Fe₂Al₉O₆(SiO₄)₄(O,OH)₂

• twinning looks like a cross (or X)

Question 7

Titanite

Answer 7

CaTiSiO₅

Question 8

Chloritoid

Answer 8

Fe₂Al4O₂(SiO₄)₂(OH)₄

• small black, platy

Question 9

Epidote

Answer 9

Ca₂(Al, Fe)₃O(SiO₄)(Si₂O₇)OH

• pistachio colour
• perfect 1 direction cleavage

Question 10

Lawsonite

Answer 10

CaAl₂(Si₂O₇)(OH)₂·H₂O

• two perfect cleavges that twin
• subtle pink

Question 11

Vesuvianite

Answer 11

Ca₁₀(Mg, Fe)₂Al₄(SiO₄)₅(Si₂O₇)₂(OH)₄

• tetragonal crystals
• tilted in light you can see a peacock blue (only in a few samples)
• shiny

Question 12

Beryl

Answer 12

Be₃Al₂(Si₆O₁₈)

• aquamarime
• striated lengthwise

Question 13

Cordierite

Answer 13

(Mg, Fe)₂Al₄Si₅O₁₈

• dichroism (peacock colours when tilted in light, but you have to really concentrate

Question 14

Tourmaline

Answer 14

(Na, Ca)(Li, Mg, Al)(Al, Fe, Mn)₆(BO₃)₃(Si₆O₁₈)(OH)₄

• hexagonal crystals striated lengthwise,columnar
• long, prismatic