Pegmatites

Question 1

granatic pegmatites

Answer 1

a rock consisting of large crystals of quartz and feldspar that form predominately by magmatic processes

Question 2

industrial source of? (5)

Answer 2

micas
feldspars
quartz
lithium
gem-quality minerals

Question 3

what shape do pegmatites tend to be?

Answer 3

dyke shaped

Question 4

rare-metals that can occur in pegmatites? (5)

Answer 4

Allanite (Ce)
Beryl (Li)
Columbite (Nb)
Tourmaline (Li, B)
Uraninite (U)

Question 5

6 characteristics of Granatic Pegmatites

Answer 5

1) giant crystals
2) Quartz and Feldspar form together/intergrowth
3) presence of Aplite
4) zones/layers with characteristic mineralogy (can be monomineralic)
5) cleavlandite albite
6) rare element minerals (Tourmaline, Lithium)

Question 6

Pegmatites crystallize from_____?

Answer 6

H2O bearing silicate melts

Question 7

the coarse grained nature of Pegmatites is the result of?

Answer 7

crystal growth in aqueous solutions
- during cooling, volatile concentration in magma lowers magma viscosity which accounts fro the abnormally sized crystals

Question 8

What allows pegmatite crystals to grow larger in a shorter amount of time?

Answer 8

the freedom of ion-motion in aqueous solution

Question 9

what 3 elements are important in the growth of pegmatites?

Answer 9

B - Boron
P - Potassium
F - Fluorine

Question 10

Pegmatite (4)

Answer 10

the term applies to extremely coarse-grained igneous intrusive rocks, usually felsic composition

• generally with a grain size larger than 2cm
• form closer to surface than previously thought
• natural showcases of mineralogy

Question 11

Aplite

Answer 11

the same as a pegmatite, except small crystals