Pectolite | |
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General | |
Category | Silicate mineral |
Chemical formula | NaCa2Si3O8(OH) |
Crystal symmetry | Triclinic H–M Symbol 1 |
Unit cell | a = 7.99 Å, b = 7.03 Å, c = 7.03 Å; α = 90.51°, β = 95.21°, γ = 102.53°; Z = 2 |
Identification | |
Color | Colorless, whitish, grayish, yellowish |
Crystal habit | Tabular to acicular, radiating fibrous, spheroidal, or columnar; massive |
Crystal system | Triclinic Pinacoidal |
Twinning | Twin axis [010] with composition plane [100], common |
Cleavage | Perfect on {100} and {001} |
Fracture | Uneven |
Tenacity | Brittle; tough when compact |
Mohs scale hardness | 4.5 - 5 |
Luster | Silky, subvitreous |
Diaphaneity | Translucent to opaque |
Specific gravity | 2.84 - 2.90 |
Optical properties | Biaxial (+) |
Refractive index | nα = 1.594 - 1.610 nβ = 1.603 - 1.614 nγ = 1.631 - 1.642 |
Birefringence | δ = 0.037 |
2V angle | Measured: 50° to 63°, Calculated: 42° to 60° |
Dispersion | r > v weak to very strong |
References | [1][2][3] |
Pectolite is a white to gray mineral, NaCa2Si3O8(OH), sodium calcium inosilicate hydroxide. 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.
It was first described in 1828 at Mt. Baldo, Trento Province, Italy and named from the Greek pektos – "compacted" and lithos – "stone".[2][3]
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.