Igneous

Question 1

Igneous rock description:

Answer 1

Size: E.G <187mm fine
Shape (of crystal): E.G Anhedral
Colour: E.G Dark (don’t be too specific for Igneous)
Composition: E.G 70% Augite+Horneblende, 30% Plagioclase F.
Texture: E.G Equicrystalline

Question 2

What are the igneous rock textures

Answer 2

IMPORTANT: ALL IGNEOUS ROCKS ARE CRYSTALLINE AND MUST BE DRAWN INTERLOCKING

•Equicrystalline, similar size crystals. Same cooling rate.

•Porphyritic, more than one crystal size. Phenocrysts encased in a finer ground mass (not a matrix). 2 cooling rates.

•Vesicular, Volcanic gas bubbles encased in a fine grained fast cooling ground mass (think pumice). Happens in Lava flows

•Glassy, Instantaneously cooled volcanic glass. Conchoidal structure (Example: Obsidian)

•Fragmental, Lithic fragments encased in ultra fine volcanic ash (NOT A CONGLOMERATE (somehow))

Question 3

What is a major igneous intrusion called?

Answer 3

A batholith

Question 4

What are the chunks of country rock inside the batholith called

Answer 4

Xenoliths

Question 5

What are the minor intrusions called?

Answer 5

Sills + Dykes

Question 6

What is a sill that jumps between beds called?

Answer 6

Transgressive sills

Question 7

Sills are __________ whereas Dykes are _____________

Answer 7

Sills are concordant whereas Dykes are disconcordant.

Question 8

Concordant sills flow…

Answer 8

Concordant sills flow with the bed(s)

Question 9

Disconcordant dykes go…

Answer 9

…Through the beds. Like cutting against the grain on a steak

Question 10

Baked margins are ???? Whereas chilled margins are ????

Answer 10

Baked margins are the zones of metamorphism around a Dyke or Sill whereas chilled margins are the areas of the S or D by the edges where the crystals are smaller.

Question 11

Name the lava types.

Answer 11

A’a lava (jagged surface)
Pahoehoe lava (ropey surface)
Pillow lave (underwater n shit and looks like a fucking pillow)