Minerals
A rock is a combination of minerals or mineral materials.A mineral is a naturally occurring, inorganic solid with a crystal structure and a characteristic chemical composition. Minerals are inorganic meaning that living things did not produce it. Coals are not minerals because they are formed from plant remains, also concrete and bricks are not minerals since they are made by humans. Each mineral is a unique substance with its own chemical composition and crystal structure. Only a fraction of the 4000 are common and these common minerals are called the rock forming-minerals because they make up most of the Earth’s rock.
The properties by which minerals can be identified include their crystal structure, color, streak, luster, density, hardness, fracture, and cleavage.
Crystal Structure
In each type of mineral, the atoms are arranged in a particular geometric shape called crystal structure. Each mineral has the same crystal structure but the size can vary. Many crystals form in a prism with different amount of sides.
Color
Some minerals can be identified in color. Pyrite is always golden color, pure sulfur is always yellow. Mineral colors can be deceptive since sight changes in composition can cause changes in mineral colors.
Streak
Streak is the color of a mineral’s powder, this can be found by scraping on an unglazed porcelain called streak plate. The color of the streak can differ from the mineral itself.
Luster
The luster of an mineral is the way in which its surface reflects light, this can refer to the general appearance or how shiny it is. Galena and pyrite have a metallic luster and sulfur has a greasy luster. Minerals with rough, crumbly surface has an earthy luster.
Density
The density of a mineral depends on its chemical composition. In general minerals made up of elements with higher atomic masses has more density.
Hardness
The atoms of mineral are held together by chemical bonds of different strength which cause different hardness. Hardness is the resistance of a material to scratching. The hardness of minerals are scaled through 1-10 called Mohs hardness scale, Diamond has 10 and Talc has 1. Scratch test is used symmetrically to determine the hardness. First they scratch on glass which indicates 5.5 and then geologists continue from that.
Fracture and Cleavage
The fracture of a mineral is how the mineral breaks. Other minerals fracture unevenly alonged curved or jagged surfaces. Fracture is determined by the crystalline structure of minerals and the bonds between the atom. Cleavage is a type of fracture in which the mineral tends to split along regular, well defined planes where the bond are weakest.
Other Properties
Some minerals have unusual properties. If you put few drops of hydrochloric acid on calcite, it will bubble, which indicates that it is distinguished from similar looking mineral quartz. Fluorite give off visible light when they are under ultraviolet, some mineral produce light when it is rubbed on metal.
Crystal Structure
In each type of mineral, the atoms are arranged in a particular geometric shape called crystal structure. Each mineral has the same crystal structure but the size can vary. Many crystals form in a prism with different amount of sides.
Color
Some minerals can be identified in color. Pyrite is always golden color, pure sulfur is always yellow. Mineral colors can be deceptive since sight changes in composition can cause changes in mineral colors.
Streak
Streak is the color of a mineral’s powder, this can be found by scraping on an unglazed porcelain called streak plate. The color of the streak can differ from the mineral itself.
Luster
The luster of an mineral is the way in which its surface reflects light, this can refer to the general appearance or how shiny it is. Galena and pyrite have a metallic luster and sulfur has a greasy luster. Minerals with rough, crumbly surface has an earthy luster.
Density
The density of a mineral depends on its chemical composition. In general minerals made up of elements with higher atomic masses has more density.
Hardness
The atoms of mineral are held together by chemical bonds of different strength which cause different hardness. Hardness is the resistance of a material to scratching. The hardness of minerals are scaled through 1-10 called Mohs hardness scale, Diamond has 10 and Talc has 1. Scratch test is used symmetrically to determine the hardness. First they scratch on glass which indicates 5.5 and then geologists continue from that.
Fracture and Cleavage
The fracture of a mineral is how the mineral breaks. Other minerals fracture unevenly alonged curved or jagged surfaces. Fracture is determined by the crystalline structure of minerals and the bonds between the atom. Cleavage is a type of fracture in which the mineral tends to split along regular, well defined planes where the bond are weakest.
Other Properties
Some minerals have unusual properties. If you put few drops of hydrochloric acid on calcite, it will bubble, which indicates that it is distinguished from similar looking mineral quartz. Fluorite give off visible light when they are under ultraviolet, some mineral produce light when it is rubbed on metal.