Osumilite, Muscovite and Tridymite

ID	407
Mineral	Osumilite Muscovite Tridymite
Location	Funtanafigu Quarry - Marrubiu - Sardinie - Italy
Fluorescence	LW-UV: close SW-UV: close
Mindat.org	View Osumilite information at mindat.org View Muscovite information at mindat.org View Tridymite information at mindat.org

Mindat data

ID	3039
Long ID	1:1:3039:3
Formula	`KFe₂(Al₅Si₁₀)O₃₀`
IMA Status	APPROVED GRANDFATHERED
Description	Osumilite Group. Difficult to distinguish from Osumilite-(Mg). Compare 'UM1984-35-SiO:AlCaFeKMg'. From Belakovskiy (2013), summarizing Chukanov et al. (2013): "Chemical data for osumilite in original paper (Miyashiro 1956) show that it is ...
General Appearance	In crystals, a few millimeters or less in size, black to the unaided eye, and prismatic or tabular in habit. Previously mistaken for cordierite.
Occurrence	Biotite-bearing hypersthene-plagioliparite (rhyodacite).
Discovery Year	1953
Diapheny	Transparent,Translucent
Cleavage	Indistinct, parallel and perpendicular {0001}
Tenacity	brittle
Colour	Black, dark blue, dark brown, pink, gray
Hardness (min)	5.0
Hardness (max)	6.0
About the name	Named in 1953 by Akiho Miyashiro for the Osumi Peninsula, Japan, on which the type locality is found.
Crystal System	Hexagonal
Cleavage Type	Poor/Indistinct
Morphology	Hexagonal, tabular. Well developed {0001}, {10_10}, {11_20}. Also {21_30}, {10_11}, {10_12}, {11_22}.
Twinning	Rarely, perpendicular to {0001}.
Publication Year	1953
shortcode_ima	Osm

ID	2815
Long ID	1:1:2815:4
Formula	`KAl₂(Si₃Al)O₁₀(OH)₂`
IMA Status	APPROVED GRANDFATHERED
Description	Mica Group. The most common of the Mica Group minerals, it is typically found as massively crystalline material in "books" or in flaky grains as a constituent of many rock types. It is clear with a pearly luster on cleavage faces, often having a spa...
Other Occurrences	Muscovite is common in many different rock types as a primary mineral.
Diapheny	Transparent,Translucent
Cleavage	Perfect on {001}.
Tenacity	elastic
Colour	White to colorless, silvery-white, and tinged various colors by impurities.
Hardness (min)	2.5
Hardness (max)	2.5
About the name	The earliest names attributable to muscovite include Muscovy Glass, Cat Silver, and Lapis Specularis (stone mirror); these names appearing in texts in the seventeenth century and before. The stand-alone name 'Muscovite' was used as early as 1794 by Johann Gottfried Schmeisser in his System of Mineralogy and is derived from the term "Muscovy glass," which was in common use by that time. Muscovy Province in Russia yielded sheet mica for a variety of uses. Muscovite and sometimes similar species were earlier called mica (Phillips and Kersey, 1706), glimmer (Phillips and Kersey, 1706), and isinglass (1747 according to OED) but all of these terms are still in use to some degree. It should be noted that mica, glimmer, and isinglass were also used for a variety of materials before these given dates and in those earlier times did not always indicate what would be a mineral, much less muscovite proper. Isinglass, for example, was originally used for a gelatinous bladder found in sturgeon.
Streak	White
Crystal System	Monoclinic
Cleavage Type	Perfect
Fracture type	Micaceous
Morphology	Crystals uncommon, tabular {001} with rhombic to hexagonal outlines, often bound by {221}, {_111} and {010} (hkl refer to -2M^1 polytype). Less common as prismatic, parallel to [001], with a crude hexagonal cross section. Most typically found as "books" and as flaky grains in various rocks. Sometimes in plumose or fibrous aggregates.
Twinning	Mica law twins common [310] forming six pointed stars, less common with the composition plane perpendicular to {001} (hkl refer to -2M^1 polytype).
shortcode_ima	Ms

ID	4015
Long ID	1:1:4015:6
Formula	`SiO₂`
IMA Status	APPROVED GRANDFATHERED
Description	Tridymite is a low pressure, mostly high-temperature-stable polymorph of silica that can also form or persist metastably at low temperatures. The high-temperature form occurs most notably as vapour-deposited, platey crystals in vesicles in some volcani...
Other Occurrences	Vapor phase deposition in vesicles and lithophysae, phenocrysts in volcanic rocks, contact metamorphosed sandstones.
Diapheny	Transparent,Translucent
Cleavage	[0001] Indistinct, [1010] Imperfect
Tenacity	brittle
Colour	Colourless, white, yellowish white, or grey
Hardness (min)	6.5
Hardness (max)	7.0
Luminescence	Non-fluorescent
Lustre	Vitreous
About the name	From the Greek "Tridymos", triplet, alluding to its common twinning as trillings.
Streak	White
Crystal System	Triclinic
Cleavage Type	Poor/Indistinct
Fracture type	Conchoidal
Morphology	Pseudohexagonal plates, wedge-shaped, tabular.
Twinning	Trilling, multiple contact twins or simple twins on {10_16} and contact or penetration twins on {30_34}
Thermal Behaviour	High tridymite or β-tridymite forms between 870 and 1470°C.
Comment Luster	May be pearly on {0001}
Publication Year	1868
shortcode_ima	Trd

Price: € 20

Dimensions: Not registered

Weight: 73 g

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Notes:

Symbol	Element
Al	Aluminium
Fe	Iron
H	Hydrogen
K	Potassium
O	Oxygen
Si	Silicium

Osumilite, Muscovite and Tridymite

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