| Pectolite | |
| Category: | Inosilicate mineral |
| Formula: | NaCa2Si3O8(OH) |
| Imasymbol: | Pct[1] |
| System: | Triclinic |
| Class: | Pinacoidal (same H-M symbol) |
| Symmetry: | P |
| 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 |
| Color: | Colorless, whitish, grayish, yellowish |
| Habit: | Tabular to acicular, radiating fibrous, spheroidal, or columnar; massive |
| Twinning: | Twin axis [010] with composition plane [100], common |
| Cleavage: | Perfect on and |
| Fracture: | Uneven |
| Tenacity: | Brittle; tough when compact |
| Mohs: | 4.5 – 5 |
| Luster: | Silky, subvitreous |
| Streak: | White |
| Diaphaneity: | Translucent to opaque |
| Gravity: | 2.84 – 2.90 |
| Opticalprop: | Biaxial (+) |
| Refractive: | nα = 1.594 – 1.610 nβ = 1.603 – 1.614 nγ = 1.631 – 1.642 |
| Birefringence: | δ = 0.037 |
| 2V: | 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), 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. There is also a whitish form of the mineral from Alaska that is sometimes marketed as 'Alaska jade'.
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.