subconchoidal

subconchoidal

[¦səb·kən′kȯid·əl]
(geology)
Pertaining to a fracture that is partly or vaguely conchoidal in shape.
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Formula: MnCO3 Crystal system: hexagonal Space group: R3c Hardness: 3.5-4.0 Specific gravity: 3.70 Cleavage: {1011} perfect Fracture: uneven to subconchoidal Tenacity: brittle Notable locality in Canada: Mont-Saint-Hilaire, Quebec Name: from the Greek rhodon meaning "rose," and chrosis meaning "colouring."
199D); streak is off-white to cream (and resinous looking); luster is resinous to greasy; diaphaneity is translucent; non-fluorescent; Mohs hardness is estimated at 3-4; tenacity is malleable; fracture is subconchoidal; cleavage and parting are not evident; calculated density is 7.212 g/[cm.sup.3] (for empirical formula and unit-cell parameter refined from powder data).
Lafossaite is malleable with a subconchoidal fracture, no observable cleavage or parting, and is non-fluorescent under both longwave and shortwave ultraviolet light.
Fracture: subconchoidal. Density: not measured because of strong chemical zoning, 3.40 g/[cm.sup.3] (calc.).
Fracture: uneven to subconchoidal. Density: could not be measured, 4.21 g/[cm.sup.3] (calc.).
Fracture: subconchoidal. Density: 2.74 g/[cm.sup.3] (meas.), 2.75 g/[cm.sup.3] (calc.).
Fracture: uneven to almost subconchoidal. Density: could not be measured because of the small amount of material, 3.41 g/[cm.sup.3] (calc.).
Arakiite is megascopically indistinguishable from either hematolite or dixenite and possesses the following physical properties: steak is pale brown; lustre is resinous to submetallic; diaphaneity is opaque (masses) to translucent (thin edges); non-fluorescent; hardness is estimated at 3-4; cleavage is {001} perfect; tenacity is brittle; fracture is uneven, almost subconchoidal; calculated density is 3,41 g/[cm.sup.3] (for empirical formula and unit-cell parameters derived from crystal structure).
Fracture: subconchoidal. Density: 3.05 g/[cm.sub.3] (meas.), 3.06 g/[cm.sub.3] (calc.).
Fracture: subconchoidal. Density: 3.57 g/[cm.sup.3] (meas.), 3.52 g/[cm.sup.3] (calc.).