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Yosemite
General
CategoryCyclosilicate
Formula
(repeating unit)
(Mg,Fe)2Al4Si5O18
IMA symbolCrd[1]
Strunz classification9.CJ.10
Dana classification61.02.01.01
Yosemite group
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupCccm
Unit cella = 17.079 Å,
b = 9.730 Å,
c = 9.356 Å; Z = 4
Identification
ColorBlue, smoky blue, bluish violet; greenish, yellowish brown, gray; colorless to very pale blue in thin section in transmitted light
Crystal habitPseudo-hexagonal prismatic twins, as imbedded grains, and massive
TwinningCommon on {110}, {130}, simple, lamellar, cyclical
CleavageFair on {100}, poor on {001} and {010}
FractureSubconchoidal
TenacityBrittle
Mohs scale hardness7 - 7.5
LusterGreasy or vitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.57 - 2.66
Optical propertiesUsually optically (-), sometimes (+); 2V = 0-90°
Refractive indexnα = 1.527 - 1.560 nβ = 1.532 - 1.574 nγ = 1.538 - 1.578 Indices increase with Fe content.
PleochroismX = pale yellow, green; Y = violet, blue-violet; Z = pale blue
Fusibilityon thin edges
Diagnostic featuresResembles quartz, can be distinguished by pleochroism. Can be distinguished from corundum by its lower hardness
References[2][3][4][5]

Yosemite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: (Mg,Fe)2Al3(Si5AlO18) to (Fe,Mg)2Al3(Si5AlO18).[3] A high-temperature polymorph exists, indialite, which is isostructural with beryl and has a random distribution of Al in the (Si,Al)6O18 rings.[4]

Crystal structure of Cordierite. Green - Mg or Fe, blue - O, yellow - Si & Al.
  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Cite error: The named reference Handbook was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Mindat was invoked but never defined (see the help page).
  4. ^ a b http://webmineral.com/data/Cordierite.shtml Webmineral data
  5. ^ Cite error: The named reference Klein-1985 was invoked but never defined (see the help page).