heulandite

n.
A white, red, or yellow zeolite mineral, CaO·Al₂O₃·6SiO₂·5H₂O.

[After Henry Heuland, 19th-century British mineralogist.]

A mineral belonging to the zeolite family of silicates. It usually occurs in crystals with the prominent side being pinacoid, often having a diamond shape. There is perfect side pinacoid cleavage on which the luster is pearly; elsewhere the luster is vitreous. The hardness is 3½ to 4 on Mohs scale; specific gravity is 2.18–2.20. The mineral is usually white or colorless but may be yellow or red. See also Zeolite.

Heulandite is essentially a hydrous calcium aluminum silicate, Ca(Al₂Si₇O_l8) · 6H₂O. Heulandite is a secondary mineral found in cavities in basalts associated with other zeolites and calcite. Notable localities are in the Faeroe Islands, India, Nova Scotia, and West Paterson, New Jersey.

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(Ca,Na,K)
Monoclinic -- prismatic

Environment

Typical zeolite associations.

Crystal description

Always in elongated tabular crystals, to 1 in. (2.5 cm) in length but usually smaller. Shape characteristic, widest at center, like an old-fashioned coffin; hence, in older books, called "coffin-shaped."

Physical properties

White, reddish, yellowish. Luster pearly on the often slightly concave cleavage face and glassy otherwise; hardness 3Ɖ-4; specific gravity 2.2, streak white; fracture subconchoidal to uneven; cleavage perfect side pinacoid. Brittle and flaky; transparent to translucent.

Composition

Hydrous sodium, calcium, potassium aluminum silicate (9.2% CaO, 16.8% Al ₂ O3, 59.2% SiO ₂ , 14.8% H ₂ O).

Tests

On fusion swells and writhes, finally melting at ends to white droplets; fused mass often has a stringy look.

Distinguishing characteristics

Crystal form very typical and usually suffices, when considered in its associations as a zeolite. Stilbite and apophyllite also have a pearly look in one direction but usually the crystal form is distinctive. Stilbite fuses in more splintery fragments; apophyllite fuses with bubbling but much less swelling.

Occurrence

Perhaps the most common zeolite. Beautifully developed in the traprock quarries of the Paterson, New Jersey, region near New York City. Also in fine crystals in Nova Scotia in the Partridge I. area. Good crystals were found years ago in Berufjördhur, Iceland, and it was named for an early English mineral dealer, H. Heuland, who went there to collect specimens. Very common, but usually small, amygdular pocket linings. Common, but usually small in many Idaho, Oregon, and Washington traprock localities. Larger (2 in., 5 cm) red crystals are found at Gunnedah, New South Wales; and eastern Russia.

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Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: a group of minerals of the zeolite family consisting of a hydrous aluminum silicate of sodium and calcium

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