GEOLOGY GRP5

rock

is a naturally occurring solid aggregate of one or more minerals or mineraloids. This means it consists of single or multiple minerals packed closely together. The Earth’s crust is solid rock, while the molten rock of the mantle is known as magma.

Igneous rocks

form when molten rock (magma or lava) cools and solidifies.

Metamorphic rocks

result when existing rocks are changed by heat, pressure, or reactive fluids, such as hot, mineral-laden water. Most rocks are made of minerals containing silicon and oxygen, the most abundant elements in the Earth’s crust

Igneous rocks

form through the cooling and solidification of magma or lava. These rocks are distinctly different from sedimentary and metamorphic rocks, which originate from the deposition of material at the Earth’s surface and the transformation of existing rocks under pressure and temperature changes

Crystalline Texture

: They often have a crystalline texture due to the interlocking of crystals that form as the molten rock cools.

Hardness and Density

: Most igneous rocks are hard and dense.

Mineral Content

: They contain a variety of minerals, including Granite, Syenite, Diorite, Gabbro, Pegmatite, Dolerite, and Basalt

Color Variations

: Their color ranges from light (in rocks with high silica content) to dark (in rocks with low silica content)

Mid-Ocean Ridges

: Basaltic rocks form as magma rises and cools at these spreading centers

Volcanic Arcs

: Arcs are associated with subduction zones, where andesites and rhyolites are common.

Hot Spots

: The Hawaiian Islands, where basaltic lava flows are typical, are an example of a hot spot.

Continental Crust

: This is where granite and other plutonic rocks form

Texture

: Grain size, shape, and arrangement of crystals

Composition

: Based on the silica content, they are categorized as felsic, intermediate, mafic, or ultramafic.

Formation Environment

: This is whether they are volcanic or plutonic

Intrusive Rocks

- Also known as Plutonic Rocks are rocks that are formed when magma cools down inside the Earth forming slow process cycle which gives the minerals inside the rock time to grow large crystals

Extrusive Rocks

- Also known as Volcanic Rocks are rocks that are formed when magma erupts reaching the Earth’s surface as lava. On the surface, it cools down quickly resulting in small or no visible crystals.

GRANITE

-Coarse or medium-grained intrusive igneous rock that is rich in quartz and feldspar; it is the most common plutonic rock of the Earth’s crust, formed by the cooling of magma (silicate melt) at depth. It forms from the slow crystallization of magma below Earth’s surface.

GRANITE

geared to the fluctuating market for curbing in highway construction and veneer used in the facing of large industrial and commercial buildings

SYENITE

-An intrusive igneous rocks essentially composed of an alkali feldspar and a ferromagnesian mineral. A special group of alkali syenites is characterized by the presence of a feldspathoid mineral such as nepheline, leucite, cancrinite, or sodalite.

Diorite

is an intrusive igneous rock composed primarily of plagioclase feldspar and smaller amounts of mafic minerals like hornblende and biotite. It has a phaneritic texture, meaning its interlocking crystals can be seen with the naked eye.

Diorite

is intermediate in composition between felsic granite and mafic gabbro. It is known for having a characteristic ‘salt and pepper’ appearance. It is one of the most common rock in the world, but the reason why it’s not well known is because it is often confused with granite.

Gabbro

is a type of intrusive igneous rock that forms when magma is cooled slowly in the Earth’s crust. It is made up of interlocking crystals of plagioclase feldspar and pyroxene. The word was first used in the 18th century and comes from the Italian word which means “a dark, igneous rock”

Gabbro

is usually black, greenish-black, or blue-gray in color and has a composition similar to basalt. However, it contains more plagioclase than basalt and is therefore lighter in color.

Pegmatite

is an intrusive igneous rock defined by its very large, interlocking crystals that can range in size from 1 cm to over 1 meter. It is usually primarily composed of quartz, feldspar, and mica, but often includes rarer minerals and gemstones. It forms in the last stages of magma crystallization

Pegmatite

has very large, interlocking crystals, generally over 1 cm in size but usually much larger than that. The crystals are interlocking, with no space between them. It usually has an overall light color due to its mineralogy and lacks any internal structural features like layering or banding.

DOLERITE

Also known as diabase, is a type of intrusive igneous rock that holds significance in the field of geology due to its unique characteristics and formation process. It is an intrusive rock, which means it forms from molten magma that cools and solidifies beneath the Earth’s surface.

DOLERITE

Diabase is often confused with basalt due to their similar appearances, but they have distinct mineral compositions and cooling histories. Diabase mineral composition is made out of plagioclase feldspar, pyroxene minerals (primarily augite), and may contain olivine, magnetite, and apatite.

Basalt

, extrusive igneous (volcanic) rock that is low in silica content, dark in colour, and comparatively rich in iron and magnesium. Some basalts are quite glassy (tachylytes), and many are very finegrained and compact. It is more usual, however, for them to exhibit porphyritic structure, with larger crystals (phenocrysts) of olivine, augite, or feldspar in a finely crystalline matrix (groundmass). Olivine and augite are the most common porphyritic minerals in basalts; porphyritic plagioclase feldspars are also found.

Andesites

- fine-grained igneous rock that forms when the magma is erupted onto the surface and is crystallized quickly.

Rhyolites

- felsic extrusive rock and due to its high silica content

Felsic

- rocks are rich in silica (over 65%) and contain a high proportion of lighter minerals like quartz and feldspar.

Intermediate

- rocks consist of roughly equal amounts of felsic and mafic minerals, with silica content typically between 52% and 65%.

Mafic

- have a lower silica content (45-52%) and are rich in iron and magnesium. The term “mafic” combines “magnesium” and “ferric” (iron)

Ultramafic

- have the lowest silica content (less than 45%) and are very rich in iron and magnesium minerals

Quartz

- widely distributed mineral of many varieties that consists primarily of silica, or silicon dioxide (SiO2)

Feldspar

- any of a group of aluminosilicate minerals that contain calcium, sodium, or potassium

Ferromagnesian mineral

- Silicate minerals in which cations of iron and magnesium form essential chemical components. The term is used to cover such minerals as the olivines, pyroxenes, amphiboles, and the micas, biotite and phlogopite

Feldspathoid mineral

nepheline, leucite, cancrinite, or sodalite- The name for a group of framework silicate minerals which are similar to feldspars in their structure but contain less silica per formula unit.

Plagioclase feldspar

- series of framework silicate minerals in feldspar group. It is a continuous series of solid solutions known as the plagioclase feldspar series, rather than a specific mineral with a particular chemical composition.

Hornblende

- a field and classroom name used for a group of dark-colored amphibole minerals found in many types of igneous and metamorphic rocks.

Biotite

- is a name used for a large group of black mica minerals that are commonly found in igneous and metamorphic rocks.