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Pectolite

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Pectolite
General
CategoryInosilicate mineral
Formula
(repeating unit)
NaCa2Si3O8(OH)
IMA symbolPct[1]
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H-M symbol)
Space groupP1
Unit cella = 7.99 Å, b = 7.03 Å,
c = 7.03 Å; α = 90.51°,
β = 95.21°, γ = 102.53°; Z = 2
Identification
ColorColorless, whitish, grayish, yellowish
Crystal habitTabular to acicular, radiating fibrous, spheroidal, or columnar; massive
TwinningTwin axis [010] with composition plane [100], common
CleavagePerfect on {100} and {001}
FractureUneven
TenacityBrittle; tough when compact
Mohs scale hardness4.5 – 5
LusterSilky, subvitreous
StreakWhite
DiaphaneityTranslucent to opaque
Specific gravity2.84 – 2.90
Optical propertiesBiaxial (+)
Refractive indexnα = 1.594 – 1.610 nβ = 1.603 – 1.614 nγ = 1.631 – 1.642
Birefringenceδ = 0.037
2V angleMeasured: 50° to 63°, Calculated: 42° to 60°
Dispersionr > v weak to very strong
References[2][3][4]

Pectolite is a white to gray mineral, NaCa2Si3O8(OH), a sodium calcium hydroxide inosilicate. It crystallizes in the triclinic system typically occurring in radiated or fibrous crystalline masses. It has a Mohs hardness of 4.5 to 5 and a specific gravity of 2.7 to 2.9. A highly sought-after variety known as larimar, is a pale to sky blue. There is also a whitish form of the mineral from Alaska that is sometimes marketed as 'Alaska jade'.

Occurrence

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Pectolite var. Larimar

It was first described in 1828 at Mount Baldo, Trento Province, Italy, and named from the Greek pektos – "compacted" and lithos – "stone".[3][4]

It occurs as a primary mineral in nepheline syenites, within hydrothermal cavities in basalts and diabase and in serpentinites in association with zeolites, datolite, prehnite, calcite and serpentine. It is found in a wide variety of worldwide locations.

See also

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References

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  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. ^ Handbook of Mineralogy
  3. ^ a b Mindat w/ localities
  4. ^ a b Webmineral
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