Silicate mineral + Igneous rock Identification 2

Granite

Texture: coarse-grained
Mineralogy: Quartz, Biotite, Muscovite
Color: grey, tan, and/or red with black & clear shiny specks over base colors
Hardness: 6 - 7; white streak

Diorite

Texture: coarse-grained
Mineralogy: Plagioclase, biotite
Color: think “dalmation”, salt & pepper coloring, covered in dark grey and light grey/white spots
Hardness: 5.5 - 6, bluish-black streak

Gabbro

Texture: coarse-grained
Mineralogy: Plagioclase, Olivine, Hornblende
Color: dark-grey with light grey or white spotting throughout; darker than diorite
Hardness: 6 - 7, black streak

Peridotite

Texture: coarse-grained
Mineralogy: Olivine, Pyroxene
Color: light to dark green or greenish-brown, sometimes light olive yellow
Hardness: 6.5 - 7, white streak

Pumice

Texture: rough, abrasive texture with numerous vesicles/cavities, silky luster
Mineralogy: augite, horneblend

Color: white, cream, blue or grey, to green-brown or black
Hardness: 6 - 6.5, white streak

lighter than tuff

Rhyolite

Texture: generally glassy & fine-textured, but may contain larger mineral crystals
Mineralogy: Quartz, Biotite

Color: light grey or tan to pinkish, can sometimes have white speckles
Hardness: 6.5 - 7, colorless streak

light weight, has shiny specks inside

Obsidian

Texture: Glassy/shiny, smooth feel
Mineralogy: volcanic glass, no minerals
Color: black

Tuff

Texture: Pyroclastic, mix of pumice, ash, and rock shards
Mineralogy: Quartz, Plagioclase
Color: light to medium-grey or pinkish
Hardness: 4 - 6, white streak

other: feels very light

Andesite

Texture: fine to coarse grained
Mineralogy: Plagioclase, quartz, horneblend

color: light to dark grey-tan, contains larger crystals inside like diorite

hardness: 7, light grey to off-white streak

Basalt

Texture: Aphanitic; very fine-grained
Mineralogy: Plagioclase, Olivine, Hornblende, biotite

Hardness: 5 - 6, dark streak
color: dark to medium-grey, sometimes white specks inside
Other: almost “soapy” feel

Scoria

Composition: Intermediate - Mafic
Texture: Vesicular, holey & rough
Formation Process: Extrusive; volcanic glass w/ gas pockets
Mineralogy: Olivine, Plagioclase
Other: Low specific gravity; dark grey to reddish color

muscovite

hardness: 2.5-3.5
cleavage: perfectly basal
luster: vitreous to pearly
color: pale yellow, brown, greenish
other notes: plate-like

quartz

hardness: 7
cleavage: six sided prism
luster: crystalline
color: colorless (clear), white, various shades of purple, pink, brown, gray, black
other notes: color depends on trace elements

hornblende

hardness: 5-6
cleavage: two directions at 60 and 120 degrees on shiny side
luster: vitreous to dull
color: black to dark green or brown, sometimes with diff. colored specks
other notes: texture either bladed crystals or fibrous masses

biotite

hardness: 2.5-3.5
cleavage: perfectly basal (single horizontal plane)
luster: vitreous (glass-like) to pearly
color: black to dark green, like a phone screen
other notes: sheet like

augite

hardness: 5-6
cleavage: two directional at 90 degrees on shiny side
luster: vitreous (shiny, glass-like) to full
color: black, green, brown
other notes: shorter name, chunkier mineral, looks like charcoal

olivine

hardness: 6.5-7
cleavage: absent
luster: vitreous
color: deep olive-green to yellow green
other notes: misshapen, granular texture

plagioclase

hardness: 6
cleavage: 2 directions, at 90 degrees
luster: vitreous to pearly
color: white, grey, blue green with parallel veins
other notes: almost like a crystal

orthoclase

hardness: 6
cleavage: 2 directions, usually at 90 degrees
luster: vitreous to pearly
color: pink, can be whitish
other notes: block-like, looks like muscle tissue