Igneous Rocks Flashcards
Igneous rock
Any rock that has formed from a molten material
Euhedral Crystal
Good crystal faces
Equant crystals
Crystals have all axis the same length
Sub-equant crystals
Crystals where all axis are almost the same length
Prismatic crystals
Crystals have 4 or more sides then same length elongated in 1 direction
Anhedral crystals
Poorly formed crystal faces
Sub-hedral crystals
Some well formed crystal faces and some poorly formed faces
Igneous texture
The overall view of crystal size and shape
Equicrystaline texture
Equal size crystals
Vesicular texture
Bubbles trapped in lava
Amygdaloidal texture
Infilled vesicles
Flow banding
Layers of dark and light minerals aligned due to separation in the lava flow
Porphyritic texture
2 distinct crystal faces
Ophilitic texture
Elongated crystal enclosed in another crystal
Cumulative texture
Crystals which have settled out of magma
Magma
Molten rock underground
Lava
Molten rock above ground
The melting point of silicic material
800°c
Enclave
Boobs of magma surrounded by magma of a different comp
Exsolition
Brought out of solution
Intrusive igneous rock
These crystallise below the surface to form structures called intrusions
Concordant intrusion
Intrudes along bedding planes
Discordant intrusion
Cuts across bedding planes
Country rock
Rocks that magma intrudes
Sill
Sheet like concordant intrusions
Dyke
Sheet like discordant intrusions
Ring complex
Dykes that form ring like structures
Come sheets
Pressure from magma forcing upwards fractures that fill with magma
Ring dyke
Magma forced along faults
Volcanic plug
Magma crystallising in the volcano vent
Chilled margin
When he edge of the igneous intrusion next to the country rock rapidly cools allowing small crystals to form
Baked margin
The area of the country rock adjacent to a minor intrusion that gets altered by the heat from the intrusion
