Crystals with a recognisable shape, can grow freely and is not stopped by any pre-existing crystals
Subhedral
Has some recognisable shape, partially stopped as they grow around pre-existing crystal
Anhedral
No regular shape, controlled by the arrangement and orientation of surrounding pre-existing crystals
Equicrystalline
All crystals are the same size
Porphyritic
Produced when the rock has has two stages of cooling,
Large crystals called Phenocycsts
Smaller Crystals called Groundmass
Glassy
No crystals - rapid cooling
Vesicular
Gas bubbles get trapped, leaving holes in the rock.
Amygdaloidal
Vesicles are filled by minerals precipitated from groundwater.
Partially filled vesicles are called geodes
Flow Banding
Bands of light and dark minerals are produced that lie parallel to the lava flow - Rhyolite
Tuff & Tuff Breccia
Rock equivalent of volcanic ash - Breccia comprises of rock and ash that are created by an explosive eruption
Tuff & Tuff Breccia
Rock equivalent of volcanic ash - Breccia comprises of rock and ash that are created by an explosive eruptionRock equivalent of volcanic ash - Breccia comprises of rock and ash that are created by an explosive eruption
