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The basic level of definition is that of mineral species, each of which is distinguished from the others by unique chemical and physical properties. For example, quartz is defined by its formula , SiO 2 , and a specific crystalline structure that distinguishes it from other minerals with the same chemical formula (termed polymorphs ).
A range of other minerals may also be included in the mixture: [6]: 134 Yellow ochre (Goldochre) pigment. Yellow ochre, FeO(OH)·nH 2 O, is a hydrated iron hydroxide (limonite) also called gold ochre. Red ochre, Fe 2 O 3 ·nH 2 O, takes its reddish colour from the mineral hematite, which is an iron oxide, reddish brown when hydrated. [7]
The color and properties derive from a structure that is a hexagonal crystalline lattice belonging to the trigonal crystal system, crystals that sometimes exhibit twinning. Cinnabar has been used for its color since antiquity in the Near East , including as a rouge -type cosmetic , in the New World since the Olmec culture, and in China since as ...
Each mineral, depending on the orientation, may not exhibit the maximum birefringence. It is important to sample a number of similar minerals in order to get the best value of birefringence. Uniaxial minerals can look isotropic (always extinct) if the mineral is cut perpendicular to the optic axis (this situation can be revealed with the ...
Micas are translucent to opaque with a distinct vitreous or pearly luster, and different mica minerals display colors ranging from white to green or red to black. Deposits of mica tend to have a flaky or platy appearance.
Fluorite comes in a wide range of colors and has consequently been dubbed "the most colorful mineral in the world". Every color of the rainbow in various shades is represented by fluorite samples, along with white, black, and clear crystals. The most common colors are purple, blue, green, yellow, or colorless.
Mineralogy applies principles of chemistry, geology, physics and materials science to the study of minerals. Mineralogy [n 1] is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy ...
Streak plates with pyrite (left) and rhodochrosite (right). The streak of a mineral is the color of the powder produced when it is dragged across an unweathered surface. Unlike the apparent color of a mineral, which for most minerals can vary considerably, the trail of finely ground powder generally has a more consistent characteristic color, and is thus an important diagnostic tool in mineral ...