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Lustre (British English) or luster (American English; see spelling differences) is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin lux , meaning "light", and generally implies radiance, gloss, or brilliance.
Mineral tests are simple physical and chemical methods of testing samples, which can help to identify the mineral type. [1] This approach is used widely in mineralogy , ore geology and general geological mapping.
Skinner's (2005) definition of a mineral takes this matter into account by stating that a mineral can be crystalline or amorphous. [21] Although biominerals are not the most common form of minerals, [31] they help to define the limits of what constitutes a mineral proper. Nickel's (1995) formal definition explicitly mentioned crystallinity as a ...
Muscovite can be cleaved into very thin transparent sheets that can substitute for glass, particularly for high-temperature applications such as industrial furnace or oven windows. It is also used in the manufacture of a wide variety of electronics and as a filler in paints, plastic, and wallboard. It lends a silky luster to wallpaper.
Selenite typically shows vitreous luster, but may show pearly luster on cleavage surfaces. Satin spar shows characteristic silky luster. [9] Luster is not often exhibited in the rosettes, due to their exterior druse; nevertheless, the rosettes often show glassy to pearly luster on edges. Gypsum flowers usually exhibit more luster than desert roses.
Rocks are composed primarily of grains of minerals, which are crystalline solids formed from atoms chemically bonded into an orderly structure. [4]: 3 Some rocks also contain mineraloids, which are rigid, mineral-like substances, such as volcanic glass, [5]: 55, 79 that lack crystalline structure. The types and abundance of minerals in a rock ...
It is generally glassy or fine-grained in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent of granite.
In some stones, the inclusion of small, white, radially clustered crystals (spherulites) of the mineral cristobalite in the black glass produce a blotchy or snowflake pattern (snowflake obsidian). Obsidian may contain patterns of gas bubbles remaining from the lava flow, aligned along layers created as the molten rock was flowing before being ...