GEL 50L rock identification

extrusive, vesicular, porphyritic, small crystals

biotite, amphibole, pyroxene

intermediate

Andesite

Extrusive, aphanitic

pyroxene, amphibole

olivine, plagioclase

mafic, 35-65%

Basalt

-extrusive, vesicular, glassy

-volcanic glass

-felsic, intermediate

Pumice

-extrusive, vesicular, aphanitic

-volcanic rock

-mafic

Scoria

Extrusive, very glassy

volcanic glass

felsic

Obisidian

-extrusive, small crystals, pyroclastic

-quartz, feldspar, biotite

-felsic

Volcanic Tuff

-clastic

-subangular

-gravel, grain >2mm

-poorly sorted

-high energy alluvial fan

Breccia

-clastic

-subrounded

-gravel, grain >2mm

-poorly sorted

-alluvial fan, fluvial beaches

Conglomerate

-clastic

-very well rounded

-sand, 1/16-2mm

-well sorted

-fluvial aeolian

-cross bedding lamination

Sandstone

-clastic

-very well rounded

-silt, 1/256-1/16 mm

-well sorted

high fluvial energy delta

Siltstone

sedimentary

Clastic

clay <1/256 mm

Well rounded

Laminated

floodplains/lagoons/offshore

shale

-clastic

-well rounded

-clay, <1/256mm

-well sorted

-abyssal, lake fluvial environments

Claystone

-bio-chemical and clastic]

-lots ofS shells

-sub angular

-gravel >2mm

-very poorly sorted

-beach (shallow marine)

Coquina

-chemical

-ocean reef

-fine grained

-”lime mud”

Micrite

-chemical

-3.5 hardness

-glassy on cleavage

-three perfect cleavage directions

-tidal flats

Dolostone

-biochemical

-Hardness of 7

-nonclastic w/ microcrystalline structure

-deep marine

Chert

-low grade

-regional

-fine grained

-Hard, Brittle

-2.5-4 Mohs Scale

-Microcrystalline

slate

-amphibole/horneblende, quartz, feldspar

-high grade

-regional

-foilated

-Parent Rocks: shale, grantitic and volcanic rocks

-medium to coarse grained

-Hard

Gneiss

Metamorphic

-comes from mafic/ultramafic rocks

-chemical, mid-ocean ridges

-smooth and waxy

-green (but not all the way thro)

-Mottled pattern

-Smooth and Waxy

-Moderately hard 35

Serpentine

- high grade

-sugary texture

-contact metamorphism

-non foilated, medium grained

-very hard rock

-No cleavage

-clear/White *can be dif colors based on impurities

-breaks in curved shards

-glassy luster

-hardness 7

Parent Rock: Sandstone w/ predom. sandstone

-does not react w/ dilute HCl

Quartzite

-non foilated

-reacts w/ HCl

-white/whitish

-regional or contact

-calcite

Parent Rock: Limestone

Marble

-”fools gold”

-fractures w/ smooth curved surfaces

-Hardness of 6.5

-Metallic Luster

-Black streak w/ a twinge of green

Pyrite

-trigonal crystal system

-hard 6.5-7.5

-sometimes black/gray

-clastic sedimentary

tourmaline

-fairy floss appearance

-soft, fibrous

-Metamorphic

Chrystoline (asbestos)

-silicate

-viterous

-no cleavage

-conchoidal fracture, glassy luster

-trigonal crystal

Quartz

foliated appearance

perfect cleavage

oily to soapy feel

mostly green in color

metamorphic (early stage)

Chlorite

Perfect/Excellent cleavage

Hardness 5-6

Black/dark green/brown

Crystal Habit: slender prismatic to bladed crystals

Hornblende

Typ clear to white

hardness: 2

Can be scratches by fingernail

Calcium Sulfate

Gypsum

2-Directions of perfect cleavage @ 90 degrees

Grantic rocks

Often displays striation

White streak

Vitreous or Pearly

6 to 6.5

Plagioclase Feldspar

can be stratched by fingernail creates powder

soapy feel

Pearly luster

white

flakes

Talc

White Mica

One direction of perfect cleavage

Clear

Pells off into thin sheets

Muscovite Mica

Opaque

Yellowish brown streak ←ALWAYS

Yellow color

Slightly metallic→but usually earthy

Limonite

red/brownish red/purplish red

Crystal

very opaque

6.5 t0 7.5 hardness

white streak← how?

Garnet

Crystal Habit: cubes

Hardness: 2.5

Glass like luster

Perfect Cleavage

White streak

Halite

Green color, close to mountain dew

silicate

hardness 7

Olivine

“black mica”

one direction of cleavage

peels off in this sheets

almost greenish

flexible

biotite

Constituent of gabbro and basalt

black/green/brown/violet

commonly forest green

natural crystal behaviors to form short primatic crystals

cleavage angle 87 degrees

concoidal to uneven fracture

5.5 to 6 hardness

Augite

2.5 Hardness

Cubic crystal

Perfect cleavage

Metallic luster

dull gray streak

Galena

glassy shiny on crystal faces

Breaks like glass, conichodal fracture

Iridescent coloring

Opal

Glassy to pearly

6 hardness

2 perfect cleavage angles, 90, 90

Potassium Feldspar