Howlite information

Howlite
Howlite
General
Category	Inoborates
Formula; (repeating unit)	Ca2B5SiO9(OH)5
IMA symbol	How
Strunz classification	6.CB.20
Dana classification	25.3.5.1
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) ; (same H-M symbol)
Space group	P21/c
Unit cell	a = 12.82 Å, b = 9.351(1) Å ; c = 8.608(2) Å; β = 104.84(2)°; Z = 4
Identification
Color	White, colorless
Crystal habit	Massive to nodular, occurs as tabular prisms flattened parallel to [100]
Cleavage	None
Fracture	Conchoidal, uneven
Mohs scale hardness	3.5
Luster	Subvitreous, glimmering
Streak	white
Diaphaneity	Translucent
Specific gravity	2.53 – 2.59
Optical properties	Biaxial (−), colorless (transmitted light)
Refractive index	nα = 1.583 – 1.586 nβ = 1.596 – 1.598 nγ = 1.600
Birefringence	δ = 0.017
2V angle	73°
References

Howlite, a calcium borosilicate hydroxide (Ca₂B₅SiO₉(OH)₅), is a borate mineral found in evaporite deposits.^[5]

^ 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.
^ "Handbook of Mineralogy" (PDF).
^ "Howlite: Howlite mineral information and data". www.mindat.org.
^ Barthelmy, Dave. "Howlite Mineral Data". webmineral.com.
^ Howlite at Mineral Galleries

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