orthosillicates

Question 1

what are the orthosillicate minerals you need to know for the exam?

Answer 1

1. garnet
2. olivine
3. sillimanite
4. kyanite
5. andalusite
6. Zircon

Question 2

what cleavage does kyanite have?

Answer 2

GOOD cleavage in three directions

Question 3

which al-sillicate has a hardness of 7?

Answer 3

sillimanite

Question 4

what are the diagnostic properties of sillimanite?

Answer 4

• fibrous/elongated crystal habit

- hardness 7

Question 5

identify the following aluminium sillicate:
habit: 
- fibrous 
aggregation:
- granular 
colour:
brownish, grey, white 
no streak: no streak
hardness:
- 7
lustre:
- vitreous/ glassy
cleavage:
- should have one direction

Answer 5

sillimanite

Question 6

identify the following aluminium sillicate: 
habit:
- elongated 
colour:
- wide range but commonly brown
hardness:
- 7.5
cleavage:
- has two directions 
additional:
- flower twinning

Answer 6

andalusite

Question 7

which aluminium polymorph has chiastolite twinning?

Answer 7

Andalusite

Question 8

Identify the following orthsillicate:
Habit:
- has a football shaped equant/isometric habit 
- commonly subhedral habits in the had specimine 
Aggregation:
- granular in the hand specimine 
Colour:
- dark grey to red 
- no streak
Lustre:
- vitreous 
Hardness:
- 6 (scratches with quartz glass but is difficult to scratch)
Cleavage:
NO CLEAVAGE

Answer 8

Garnet

Question 9

Identify the following orthsillicate:
Habit:
- isometric/bladed
Aggregation:
- typically granular in most of the class hand specimens 
Colour:
-Vibrant green
- no streak
Lustre:
- vitreous 
Cleavage:
- no cleavage- conchoidal fracturing 
Hardness: 
- 5/6 (scratched by quartz glass)

Answer 9

Olivine

Question 10

identify the follwing orthosilolicate:
habit:
- elongated/bladed 
colour:
- distinct bluish 
lustre:
- pearly or vitreous 
hardness:
- 5/6
cleavage:
- three directions

Answer 10

kyanite

Question 11

how many cleavage directions should andalusite have?

Answer 11

two