Pectolite

From The Gemology Project
Revision as of 22:51, 17 January 2007 by Russell (talk | contribs)
(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search

Pectolite

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

Crystal System: Triclinic

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

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.

Optical and Physical Properties:

Cleavage: perfect on {100} and {001}.

Fracture: Uneven

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.

Hardness: 4.5 to 5.0

Lustre: silky, subvitreous

Optical Nature: Biaxial (+)

Refractive Index: α = 1.592 – 1.610, β = 1.603 to 1.615, γ = 1.630 – 1.645

Birefringence:

Dispersion:

Pleochroism:

Spectroscope:

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

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

Treatments:

Synthetics:

Imitations:

Occurence:

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" External Links: