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16.52: Pectolite

  • Page ID
    4952
  •  

    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 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 Dominican Republic"