Pectolite

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Pectolite
Chemical composition NaCa2Si3O8(OH)
Crystal system Triclinic
Habit Aggregate
Cleavage perfect
Fracture uneven
Hardness 5
Optic nature Biaxial +
Refractive index 1.59 - 1.63
Birefringence 0.028-0.038
Dispersion Very weak
Specific gravity 2.62 - 2.87
Lustre Silky
Fluorescence Green (SW & LW-UV)

Varietal Names: “Larimar” is a blue pectolite from the Dominican Republic; the name “Larimar” is trademarked.

Crystal Habit

Crystals are uncommon and are usually tabular. More commonly occurs as bundles of acicular needles showing either columnar or radiating fibrous structure.

Chemical composition

Sodium calcium silicate hydroxide, NaCa2Si308(OH). Minor to trace amounts of iron, potassium and copper may be present.

Diagnostics

Color

Colorless, white, pale apple green, dark green; the Larimar variety varies from white to light medium blue (similar to turquoise) to green.

Magnification

The “Larimar” type of pectolite displays opaque red dendritic hematite, inclusions of translucent to transparent square patches of calcite to 2 mm wide, sprays of transparent to translucent grey natrolite as long prisms with square cross section, opaque blebs of native copper, and opaque blebs and euhedral crystals of chalcocite, a copper sulfide Woodruff (1989). This same assemblage of accessory minerals is present in other, non-gem quality pectolite occurrences, such as the basalts of Paterson, New Jersey.

Cleavage

Perfect on {100} and {001}.

Specific Gravity

2.84 to 2.90 (measured), 2.97 (calculated).
Measurements of the specific gravity of Larimar ranged from 2.62 to 2.87; low range readings were probably a result of a inclusions of other minerals in the pectolite.

Refractive Index

nα = 1.592 – 1.610, nβ = 1.603 to 1.615, nγ = 1.630 – 1.645

Fluorescence

Woodruff and Fritsch (1989) report a turbid green fluorescence under Short Wave ultraviolet radiation and a chalky green fluorescence under Long Wave for Larimar.

Phenomenon

Larimar may exhibit localized areas that appear chatoyant resulting from oriented parallel clusters of pectolite needles.

Treatments

None known

Synthetics

None known

Imitations

None known

Occurrence

Occurs in cavities in basalts and diabases as a result of hydrothermal action.

The Larimar variety of pectolite occurs in a basalt formation about 5km west of Baoruco, Dominican Republic; the pectolite was first discovered in 1974 as stream-rounded pebbles in an adjacent river.

In 1884, Frank W Clarke reported that a number of Eskimo artifacts collected near Point Barrow, Alaska – originally believed to be jade - were, in fact, composed of a “interesting variety of compact pectolite, in two varieties, one pale apple green, the other dark green” [cited in Kunz (1892)]. Apparently the original source of the pectolite has not been found. Kunz also notes in 1887 geologist William P. Blake reported the discovery of a significant occurrence of compact, translucent pectolite that was “white, with a delicate shade of sea green” in color in Tehama County, California.

Care and Maintenance

Pectolite can be decomposed by mineral acids into a colorless silica gel; care should be exercised in the use of chemical cleaning agents.

Sources

  • Anthony, John W., Bideaux, Richard A., Bladh, Kenneth W., and Nichols, Monte C. (1990): Handbook of Mineralogy: Mineral Data Publishing, Tucson, Arizona
  • Kunz, George Fredreick (1892) Gems and Precious Stones of North America. The Scientific Publishing Company, New York NY ISBN 0486218554
  • Palache, Charles, Harry Berman & Clifford Frondel (1944): The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Seventh edition
  • Woodruff, Robert B and Fritsch, Emmanuel (1989) Gems and Gemology, Vol. 25 No. 4 pp 216-225 "Blue Pectolite From The Domininican Republic"

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