Igneous Rocks

Question 1

Texture

Answer 1

Size, shape, distribution and layering of mineral grains within a rock

Question 2

Phaneritic

Answer 2

Grain size greater than 0.25mm

Large enough to be distinguished without magnification

Question 3

Aphanitic

Answer 3

Average grain size less than 0.25mm

Small (invisible)

Question 4

Groundmass

Answer 4

Smaller grains of rock

Question 5

Phenocrysts

Answer 5

Larger grains of the rock

Question 6

Porphyritic rock (porphyry)

Answer 6

2 distinctly different sizes of grains (ground mass with phenocrysts)

Question 7

Obsidian

Answer 7

Magma cooled quickly, unable to nucleate and grow crystals - solidifies into glass

Same chemical composition as rhyolite and granite

Question 8

Tachylyte

Answer 8

Basaltic volcanism/ mama cooled very rapidly

Question 9

Vesicle

Answer 9

Round or oblong hole in an igneous rock or natural glass formed by gas trapped in the magma as it was solidifying.

Question 10

Scoria

Answer 10

Dominated by vesicles

Gas bbq with lava rock

Question 11

Pumice

Answer 11

Glassy foam of vessicles

Floats due to little bulk density

Question 12

Tephra

Answer 12

Particles ejected from volcano during explosive eruption

Said to be pyroclastic

Question 13

Pyroclastic

Answer 13

“Fire-broken” deposits

Question 14

Ignimbrite

Answer 14

Deposit associated with pyroclastic flow

Question 15

Tuff

Answer 15

General name for a deposit friend from maternal that settled out of the air from a volcanic eruption

Question 16

Xenolith

Answer 16

Piece of older rock that has become incorporated in a magma

By becoming departed from wall of magma chamber and floating into melt or plucked grim source area as magma rose where it crystallized

Question 17

Felecia

Answer 17

Magma that forms igneous rock with light toned silicate minerals