Pectolite

Pectolite
General
Category	Inosilicate mineral
Formula	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'.

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.

• Serandite – the manganese analogue

• Mineral galleries

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