8/17/2019 Igneous rock Hand Specimen
1/3
Basalt-
Black color, fine grained, conchoidal
fracture. Hemi crystalline
Structure: vesicular or amygdaloidal. olivine
and pyroxene have green color.
Texture: Usually dense with no minerals
identifiable in hand specimen; a freshly
broken surface is dull in appearance. May
be porphyrithic – ( larger crystals
are
surrounded by smaller ones)
Mineralogy: Phenocrysts are usually olivine
(green, glassy), pyroxene (black, shiny) or
plagioclase (white-grey, tabular). If olivine
is present the rock is called olivine basal.
Gabbro-
Black color, coarse grained, Holocrystalline.
Phaneric medium to coarse grained.
Equigranular, panidiomorphic .
Peridotite-
Looks like coal . Holocrystalline, Phaneritic,
medium to fine grained.
