Geos

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felsic

>65% silica, light in color

hardness

how easily the surface of a mineral can be scratched

Igneous

formed by cooling molten rock

un-ionized

no electric charge, neutral

fracture

the tendency of a crystal to break along irregular surfaces other than cleavage planes

Pearly

Whitish iridescence

rock

naturally occurring solid aggregate of minerals

negative feedbacks

working against each other, towards equilibrium

planar surface

crystal face, a flat surface

Porphyritic rocks have: (regarding cooling rate)

two stages of cooling history

Phaneritic

large (>1mm) interlocking crystals

same chemical compound as silica

quartz

Pegmatitic

exceptionally large (>1cm) crystals

composition

mineral content in rock, dicated by Silica content

anhydrous

free from water

glassy

glassy, such as obsidian

Intrusive

cooled below surface

Aphanitic is _____-cooling

fast

Vesicular

gas bubbles

mineral

building block of rocks, a naturally-occurring solid crystalline

amorphous

glassy, orderly-arranged atoms, without form

Texture

describes size and shape of grains

Splintery

appears fibrous

faster cooling rate implies the rock formed:

closer to surface

mafic

45-55% silica content, quite dark in color

intrusive

formed below surface

metallic

strong reflection off opaque surface

Aphanitic

small (<1mm) crystals

Igneous rocks typically:

hard, composed of crystals, minerals arranged at random

vitreous

like glass in appearance or physical properties

Obsidian is black, despite being felsic, because of

the bit of iron impurities it contains

conchoidal

showing smooth, curved surfaces

Phenocryst

relatively large pieces of crystal

angular unconformities

where younger sedimentary layers are deposited over older, tilted, and eroded rock layers

Polymorph

minerals with the same chemical composition but different crystal structures

greasy

oily coating look

Veins

tabular deposits of precipitated minerals in fractures

Obsidian is: (felsic, mafic, or intermediate?)

felsic

positive feedbacks

working in the same direction, either increasing or decreasing in intensity simultaneously

Intermediate

45-55% silica content, nearly 50-50 felsic-mafic, usually grey

trace elements

make up less than .1% of a mineral

silky

sheen of fibrous materials

Extrusive

cooled above surface

Even though granite has little black crystals, it is still considered felsic because

a large majority of it is composed of light-colored minerals

grains

crystalline particles

adamantine

brilliant, like diamonds

Pyroclastic

mostly composed of ash

crystal habit

the shape crystals grow

Phaneritic is _____-cooling

slow

resinous

resins, like amber

luster

the way a mineral’s surface reflects light

Native elements

naturally un-ionized pure elements

most common compound in Earth’s crust

silica

cleavage

the geometric pattern produced by split crystals along planar surfaces