Minerals in geology (2)

ROCK AND MINERAL TYPES• Minerals are chemical compounds, sometimes specified by crystalline structure as well as by composition, which are found in rocks or pulverized rocks, known as s

ROCK AND MINERAL TYPES

• Minerals are chemical compounds, sometimes specified

by crystalline structure as well as by composition, which are found in rocks (or pulverized rocks, known as sand).

• Rocks consist of one or more Minerals, and fall into three

main types depending on their origin and previous

processing history:

o Igneous rocks are ones which have solidified directly from a

molten state, such as volcanic lava

o Sedimentary rocks are ones which have been

re-manufactured from previously existing rocks, usually from the products of chemical weathering or mechanical erosion, without melting

o Metamorphic rocks are ones which result from processing,

by heat and pressure (but not melting), of previously existing sedimentary or igneous rocks

COMMON MINERALS IN THE EARTH

• AMPHIBOLE

(Ca2Mg5)Si8O22(OH)2

• FELDSPARS

ROCK AND MINERAL TYPES

• Examples of Igneous Rocks and their constituent minerals

include:

• Basalt, Gabbro, Rhyolite, Granite

o Feldspar, Quartz, Amphibole, Pyroxine, Olivine

• Basalt and Gabbro differ not in composition, but in crystallinity;

likewise Rhyolite and Granite

• Basalt and Gabbro differ in relative composition, of the five

major constituents above, from Rhyolite and Granite

• Basalt and Rhyolite have small crystals because they are

erupted by volcanoes and cool rapidly from the molten state

• Gabbro and Granite have large crystals because they cool

slowly from the molten state, underground

ROCK AND MINERAL TYPES

• Basalt/Gabbro and Rhyolite/Granite differ in their

proportions of the minerals listed above:

o Basalt and Gabbro consist mostly of Pyroxine and

Olivine Since these minerals consist largely of

magnesium and iron silicates, these rocks are

sometimes called mafic.

o Rhyolite and Granite consist mostly of Feldspar,

Quartz, and Amphibole They are, hence, sometimes

called felsic rocks.

o There is a continuous range in composition between the two extremes, of both composition and crystallinity.

ROCK AND MINERAL TYPES

• Examples of Sedimentary Rocks include Limestone,

Sandstone, and Shale.

o Limestone is mostly Calcite (CaCO3) produced by

chemical weathering of Feldspar and other silicate

minerals Limestone also is produced from the shells and skeletons of sea life (e.g plankton and coral).

o Sandstone and Shale are produced from sand (mostly quartz) and clay minerals (such as kaolinite), which result from mechanical and chemical weathering of igneous rocks.

• Examples of Metamorphic Rocks include Marble (from

Limestone) and Slate (from Shale).

The Rock Cycle