courtesy : geology
Geological material
The majority of geological data comes from research on solid Earth materials. Meteorites and other extraterrestrial natural materials are also studied by geological methods.
Mineral
Main article: Mineral
Minerals are natural occurring elements and compounds with a definite homogeneous chemical composition and ordered atomic composition.
Each mineral has distinct physical properties, and there are many tests to determine each of them. The specimens can be tested for:
- Luster: Quality of light reflected from the surface of a mineral. Examples are metallic, pearly, waxy, dull.
- Color: Minerals are grouped by their color. Mostly diagnostic but impurities can change a mineral’s color.
- Streak: Performed by scratching the sample on a porcelain plate. The color of the streak can help name the mineral.
- Hardness: The resistance of a mineral to scratching.
- Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces, and the latter a breakage along closely spaced parallel planes.
- Specific gravity: the weight of a specific volume of a mineral.
- Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing.
- Magnetism: Involves using a magnet to test for magnetism.
- Taste: Minerals can have a distinctive taste, such as halite (which tastes like table salt).
Rock
The rock cycle shows the relationship between igneous, sedimentary, and metamorphic rocks.
Main articles: Rock (geology) and Rock cycle
A rock is any naturally occurring solid mass or aggregate of minerals or mineraloids. Most research in geology is associated with the study of rocks, as they provide the primary record of the majority of the geological history of the Earth. There are three major types of rock: igneous, sedimentary, and metamorphic. The rock cycle illustrates the relationships among them (see diagram).
When a rock solidifies or crystallizes from melt (magma or lava), it is an igneous rock. This rock can be weathered and eroded, then redeposited and lithified into a sedimentary rock. It can then be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric. All three types may melt again, and when this happens, new magma is formed, from which an igneous rock may once more solidify. Organic matter, such as coal, bitumen, oil and natural gas, is linked mainly to organic-rich sedimentary rocks.
Quartz from Tibet. Quartz makes up more than 10% of the Earth’s crust by mass.
To study all three types of rock, geologists evaluate the minerals of which they are composed and their other physical properties, such as texture and fabric.
Unlithified material
Geologists also study unlithified materials (referred to as superficial deposits) that lie above the bedrock. This study is often known as Quaternary geology, after the Quaternary period of geologic history, which is the most recent period of geologic time.
Magma
Main article: Magma
Magma is the original unlithified source of all igneous rocks. The active flow of molten rock is closely studied in volcanology, and igneous petrology aims to determine the history of igneous rocks from their original molten source to their final crystallization.
