rocks and minerals

rocks

naturally occurring, aggregate of minerals, natural building block of Earth’s lithosphere, can be solid or semi-solid (magma)

how do rocks form?

rocks are constantly generated, transformed and destroyed by heat, pressure, and chemical change

rock cycle (how do igneous rocks form?)

intrusive igneous rock forms when magma crystallizes beneath the earth’s surface, which is slow cooling causing large crystals in the rock formation.

extrusive igneous rock forms when lava has erupted from volcanoes, hardening on the earth’s surface, with small crystals.

rock cycle (how do sedimentary rocks form?)

weathering and erosion, compaction and cementation (due to lithification)

rock cycle (how do metamorphic rocks form?)

form from pre-existing rocks, undergoes change due to heat and pressure

compare magma and lava

magma is inside the earth, both in the mantle and crust while lava is magma but on the surface of the crust

basaltic magma

low silica (45-75%) , is most common, has high temp and low viscosity, low gas content, creates lava fountains

rhyolitic magma

high silica (75%~) low temperature, high viscosity, high gas content

andesitic magma

properties between rhyolitic and basaltic

igneous rocks

derived from the word ‘ignis’ which means fire, forms from volcanoes

types of igneous rocks (according to texture)

intrusive/plutonic - big crystals due to slow cooling, forms underground

ex. granite

extrusive - small crystals due to fast cooling, forms on earth’s surface

ex. basalt

types of igneous rocks (according to composition)

felsic - light colored, made with feldspar and silicon

ex. granite

mafic - dark colored, made with magnesium and iron

ex. basalt

sedimentary rocks

has layers/strata, is weak and easily falls apart, can contain fossils and record Earth’s history

clastic/detrital

form by compaction of rock fragments

arranged from biggest to smallest fragment

conglomerate, breccia, sandstone, siltstone, shale

chemical

chemical precipitation of dissolved minerals

ex. rock salt, limestone, gypsum

metamorphism

changes in mineralogy, texture, chemical composition

foliated metamorphic rock

has layers because of unequal pressure

ex. slate, schist, gneiss

non foliated metamorphic rock

no bands, equal pressure in all directions

ex. marble, quartzite

contact metamorphism

rocks with presence of high temp due to magma causes bloating, change only happens where the contact is, nearer to magma chamber is higher metamorphic grade

burial metamorphism

happens deep undergound, high temp and pressure, rocks don’t melt but rearrange, usually non-foliated

regional metamorphism

found in mountain ranges, different amounts of pressure (tension, compression, shear)

minerals

natural, solid, crystalline, definite chemical composition

luster

metallic, nonmetallic (vitreous, pearly, adamantine, resinous), submetallic

color

unreliable because one mineral can have different colors, and one color can be of different minerals due to impurities

hardness

resistance of a mineral to scratching, mohs hardness scale

cleavage

tendency of mineral to split along weak/smooth planes and produce smooth surfaces

measured by three things, (quality, number of sides, cleavage habit)

streak

reveals the true color of the mineral

fracture

for minerals with no cleavage

other properties

density, taste, odor, magnetism