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The Mineral pectolite

Radiating Interconnected Pectolite

Pectolite is a unique mineral known for its interesting crystal habits. Its crystals primarily form as extremely slender and elongated densely grouped fragile fibers radiating from a central point outwards. When the fibers are very densely-packed, the result formation is as thick, globular masses. Pectolite can be tough and dense, but is often very delicate and soft to the touch. It can be dented by just touching it too hard, and thin splinters are easily broken when handled. Pectolite specimens are also known to give splinters when handling due to their slender and brittle crystals which easily break.

Chemical Formula

NaCa2Si3O8(OH)

Color

White, colorless, gray, light yellow, brown, pink, orange, salmon, and light blue. Some specimens tarnish brown or black upon exposure to air.

Crystal System

Triclinic

Properties

Streak
White
Hardness
4.5 - 5
Transparency
Transparent to translucent
Specific Gravity
2.7 - 2.9
Luster
Silky, vitreous
Cleavage
2,2 - forming at an angle near 90º
Fracture
Splintery, uneven
Tenacity
Brittle
Other ID Marks
May fluoresce yellow or orange in longwave ultraviolet light, and light yellow in shortwave.

Crystal Habits

Single crystals are very rare. When they do occur, they are elongated prismatic splinters, and are usually protrusions from dense radiating aggregates. However, small, flat, single blades do occur in a few select localities. Pectolite mainly occurs as fibrous and radiating veins, in radiating balls and tufts, in mammilary and globular masses, and in fan-liked masses radiating from a central point. Globular Pectolite occasionally fills the linings of basalt cavities and geodes.

Additional Information

Composition
Hydrous sodium calcium silicate, sometimes with some manganese
In Group
Silicates; Inosilicates
Striking Features
Crystal habits and mineral associations
Environment
Primarily in igneous environments, in cavities of basalt and as veins in seams of diabase. Also occasionally in metamorphic Serpentine deposits and in nepheline syenite deposits.
Rock Type
Igneous, Metamorphic

Varieties

 -   Light blue to blue variety of Pectolite that is found in the Dominican Republic. Also see the gemstone section on Larimar.

Uses

Pectolite is used mainly a collectors mineral. Good specimens especially from the New Jersey traprocks are increasingly hard to obtain and are sought out by mineral collectors. The light blue variety Larimar is used as a minor gemstone and is a rarity for collectors. When not cut as a gemstone, Larimar specimens are sliced and polished to highlight the colors.

More information on Larimar can be found in the gemstone section.

Noteworthy Localities

European localities include Těchlovice and Kostalov in Bohemia, Czech Republic; and Kreimbach-Kaulbach, Germany. The famous blue Larimar variety is only found in Caribbean country of the Dominican Republic, at the Filipinas Mine in Los Checheses.

The finest specimens for this mineral were found in the traprock quarries of northeastern New Jersey. Some of the best and thickest groupings came from Paterson and Prospect Park, Passaic Co. Millington, Morris Co., was known for outstanding white, pink, salmon, and yellow globular Pectolite masses that often formed in cavities and geodes. Thick radiating Pectolite veins lining seams in diabase were found in the Palisades sill at Bergen Hill, Hudson Co.; in Ft. Lee, Bergen Co.; and across the state border at Rockland Lake, Rockland Co., New York.

Other U.S. occurrences of this mineral are Magnet Cove, Garland Co., Arkansas, and Island Royale in Lake Superior, Michigan, where pink, waterworn pebbles can be found on the beach.

In Quebec, Canada, two famous localities have produced individual crystals of Pectolite that are drastically different than all others. The Jeffery Quarry, Asbestos; and Mont Saint Hilaire have produced prismatic and elongated crystals and groupings of such crystals.

Distingushing Similar Minerals

Wollastonite - Occurs in different environments.
Tremolite - Slightly harder (5 - 6), usually flexible, not usually in radiating form.
Natrolite and Mesolite - Crystals are usually larger and aggregated less densely; otherwise difficult to distinguish.


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