The chemical, physical and optical properties of natural gemstones are shown through measurements of light dispersion, hardness, density or specific gravity, cleavage, fracture, tenacity, refractive index and luster. These properties vary depending on the type of natural gemstone. For example, amethyst has a specific gravity of between 2.6 to 2.7, a hardness of seven, a refractive index of between 1.54 to 1.55 and a chemical formula of SiO2.
Hardness is graded on the Mohs hardness scale from one to 10, with talc graded at one and diamonds at 10. The specific gravity is the relationship between the stone's weight and heaviness. Cleavage is a break due to directional weakness, while fracture is irregular surface cracks. Tenacity is the strength of the stone. For example, the natural gemstone aquamarine, a type of beryl, has a formula of Be3Al2(SiO3)6, a Strunz classification (based on chemical composition) of 09.CJ.05, a formula mass of 537.50, imperfect cleavage, a fracture of conchoidal (shell-like) to irregular, a brittle tenacity, a Mohs scale hardness of 7.5 to 8, a luster of vitreous to resinous, a streak of white, a diaphaneity of transparent to translucent, a specific gravity average of 2.76, a uniaxial optical property (with one optic axis) and a refractive index of either 1.564 to 1.595 or 1.568 to 1.602.Learn More
Gneiss is formed from the high-temperature metamorphism of existing igneous rocks, generally granite or diorite. The rocks that form gneiss are exposed to extreme pressures and temperatures of between 600 and 700 degrees Celsius. These temperatures cause the individual minerals to migrate, forming distinct bands through the rock.Full Answer >
The two main methods of mineral formation are cooling and evaporation. The cooling process occurs when magmas and lavas cool and crystallize into minerals. Minerals formed through evaporation are the result of electrically charged atoms, known as ions, linking together to form crystals.Full Answer >
Tin was discovered prior to the beginning of recorded history, so its exact date of discovery is unknown. Its first known use was at the start of the Bronze Age in approximately 3000 B.C. During this time period, it was used exclusively as a component of bronze and pewter alloys.Full Answer >
Exfoliation geology is a type of rock weathering where the rock's layers peel off in whole sheets instead of grain by grain. Large-scale exfoliation occurs due to the mechanics of gravity on a curved surface, while small-scale exfoliation is due to chemical weathering.Full Answer >