Rocks and Minerals

Rocks & Minerals

REFERENCES - the following sites have provided information used on this page:

COMPOSITION OF CRUST
About Rocks & Minerals
About Minerals
BBC Rock Guide
Advanced Mineral Ref.

IGNEOUS
Feldspar - GeoMan
Bowen's Reaction Series
Phaneritic Feldspar
Rock Textures ***
Mineral Flow Chart **
Mineral ID
Mineral ID 4 Kids ***
Minerals - Slide Show

SEDIMENTARY

METAMORPHIC

The Earth's crust is predominantly comprised of 8 elements (98.5%):

Oxygen . . . . . . 46.6%
Silicon . . . . . . 27.7%
Aluminium . . . . . 8.1%
Iron . . . . . . . . . 5.0%
Calcium. . . . . . . 3.6%
Sodium . . . . . . . 2.8%
Potassium. . . . . . 2.6%
Magnesium. . . . . 2.1%

3 Types of Rocks:

Igneous - "fire formed" i.e. formed from molten rock

Feldspar 60% of the Earth's crust
Basalt
Granite

An understanding of the chemical composition of rocks is important when classifying rocks.

Most rocks contain large amounts of SiO₂. They can be further divided into two groups Mafic and Felsic.

Mafic - high in iron, magnesium, calcium - heavier elements - dark colour, more dense - olivine, pyroxene, amphibole, biotite (black) mica, and plagioclase feldspars
Mafic eruptions SiO₂ 45% - 52% high temperature >1000°C low viscosity (flows quickly) minerals: olivine, pyroxene, plagioclase quiet, flows like water, spectacular plumes
Basalt	usually found on the ocean floor relatively thin dense layers extrusive - cools quickly, on or near the surface fine grained, black, dense rock formed from molten rock in the mantle
Gabbro	intrusive obvious crystals
Scoria	frothy
Intermediate Eruptions SiO₂ 53% - 65% moderate temperature >1000°C minerals: plagioclase, amphibole, muscovite/biotite, quartz forms - andesite: extrusive, aphanitic; diorite: intrusive, phaneritic; breccias pyroclastic flows - flows of ash and debris up to several hundred kph, at hundreds of degrees Celsius
Felsic - high in silica, oxygen, and potassium, aluminium, sodium - lighter elements - light colour, less dense - quartz, muscovite (translucent) mica, and orthoclase feldspars
Felsic eruptions SiO₂ >65% low temperature 600°C. - 900°C high viscosity (sticky) minerals: potash feldspar, quartz, muscovite/biotite, amphibole very explosive
Granite	usually found in continental crust forms thick rafts that "float" on more dense basalt intrusive - cools slowly and deep below the surface "grainy" - clearly visible crystals form because it cools slowly 25% - 30% of Earth's surface formed from molten crustal rock
Rhyolite	extrusive lacks visible crystals
Pumice	frothy
Obsidian	glassy

Sedimentary
3 Types according to the origin of the sediments:

Clastic

mudstone
siltstone
sandstone
conglomerate

Organic - from "once living" material

limestone
coal

Chemical

Metamorphic

since 10/02/2002