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A range of terms are used to describe lustre, such as earthy, metallic, greasy, and silky. Similarly, the term vitreous (derived from the Latin for glass, vitrum) refers to a glassy lustre. A list of these terms is given below. Lustre varies over a wide continuum, and so there are no rigid boundaries between the different types of lustre.
This glass is formed naturally by the rapid cooling of molten basalt. It is a type of mafic igneous rock that is decomposable by acids and readily fusible. [citation needed] The color is a black or dark-brown, and it has a greasy-looking, resinous luster. It is very brittle and occurs in dikes, veins, and intrusive masses.
Luster: Vitreous to resinous: Streak: Light orange to light brown sometimes even an alien magenta: Diaphaneity: Nearly opaque, transparent in thin fragments: Specific gravity: 6.63 – 7.20: Optical properties: Uniaxial (−) Refractive index: n ω = 1.790 – 1.840 n ε = 1.780 – 1.820: Birefringence: δ = 0.010 – 0.020: Alters to ...
Vitreous lustre, a glassy luster or sheen on a mineral surface; Biology. Vitreous body, a clear gel that fills the space between the lens and the retina in ...
Non-metallic lustres include: adamantine, such as in diamond; vitreous, which is a glassy lustre very common in silicate minerals; pearly, such as in talc and apophyllite; resinous, such as members of the garnet group; silky which is common in fibrous minerals such as asbestiform chrysotile. [74]
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Its lustre, which may be vitreous to resinous, together with its crystal system, may lead to a confusion with zircon (ZrSiO 4), the latter having a similar crystal structure and with which xenotime may sometimes occur. Xenotime has two directions of perfect prismatic cleavage and its fracture is uneven to irregular (sometimes splintery).
Color varieties are colorless, white, gray, yellowish or pinkish, and can be transparent to translucent. Whitlockites exhibit a vitreous to resinous luster. The typical habit of whitlockite is rhombohedral crystals, but whitlockite can also rarely be tabular. The crystal habit of whitlockite also ranges from coarse granular to earthy. [15]