Pectolite
Pectolite | |
---|---|
General | |
Category | Inosilicate mineral |
Formula (repeating unit) | NaCa2Si3O8(OH) |
IMA symbol | Pct[1] |
Crystal system | Triclinic |
Crystal class | Pinacoidal (1) (same H-M symbol) |
Space group | P1 |
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 |
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 |
Streak | White |
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 | [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
[edit]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
[edit]- Serandite – the manganese analogue
References
[edit]- ^ 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
- ^ a b Mindat w/ localities
- ^ a b Webmineral