Pectolite

(repeating unit)NaCa₂Si₃O₈(OH)IMA symbolPct^[1]Crystal systemTriclinicCrystal classPinacoidal (1)
(same H-M symbol)Space groupP1Unit cella = 7.99 Å, b = 7.03 Å,
c = 7.03 Å; α = 90.51°,
β = 95.21°, γ = 102.53°; Z = 2IdentificationColorColorless, whitish, grayish, yellowishCrystal habitTabular to acicular, radiating fibrous, spheroidal, or columnar; massiveTwinningTwin axis [010] with composition plane [100], commonCleavagePerfect on {100} and {001}FractureUnevenTenacityBrittle; tough when compactMohs scale hardness4.5 – 5LusterSilky, subvitreousStreakWhiteDiaphaneityTranslucent to opaqueSpecific gravity2.84 – 2.90Optical propertiesBiaxial (+)Refractive indexn_α = 1.594 – 1.610 n_β = 1.603 – 1.614 n_γ = 1.631 – 1.642Birefringenceδ = 0.0372V angleMeasured: 50° to 63°, Calculated: 42° to 60°Dispersionr > v weak to very strongReferences^[2][3][4]

Pectolite is a white to gray mineral, NaCa₂Si₃O₈(OH), 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. The gemstone variety, larimar, is a pale to sky blue.

Occurrence

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

• Serandite – the manganese analogue

References

External links

• Mineral galleries