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The Mineral natrolite

Delicate Acicular Natrolite Needles

Natrolite is a common member of the zeolite group, and is known for its needle-like crystal habits. It is closely related to Mesolite and Scolecite, and can appear very similar to them. Chemical analysis or optical tests are sometimes required to distinguish Natrolite from the "needle zeolites" Mesolite and Scolecite. In fact, sometimes a single crystal may contain part of each mineral within different zones of the same crystal. Natrolite in acicular form is very brittle and easy broken, so care should be exercised when handling specimens. Natrolite is named for the Greek word "natron", in allusion to its sodium content, and "lithos" for stone.

Chemical Formula

Na2Al2Si3O10 · 2H2O

Color

White, colorless, off-white, light gray. Rarely yellow, pink, orange or light brown.

Crystal System

Orthorhombic

Properties

Streak
Colorless
Hardness
5 - 5.5
Transparency
Transparent to translucent
Specific Gravity
2.2 - 2.3
Luster
Silky in dense crystal groupings; vitreous or pearly in individual crystals.
Cleavage
1,1
Fracture
Uneven
Tenacity
Brittle
Other ID Marks
May be fluorescent white, yellow, or light blue.

Crystal Habits

Most often in dense acicular and radial groupings, with individual slender crystals protruding from the grouping. Uncommon in large, elongated prismatic crystals, which will have a short pyramidal termination. Crystals may also form as spiky aggregates of rounded, ball-shaped hemispheres and dense tufts, as well as globular formations with distinct micro-terminations. Also columnar, in grainy masses of slender crystals, in dense massive formation, reticulated, as linings of cavities with a spiky or fibrous interior, and in veins.

3D Crystal Atlas

Additional Information

Composition
Hydrous sodium aluminum silicate
In Group
Silicates; Tectosilicates; Zeolite Group
Striking Features
Crystal habits and association with other zeolites.
Environment
Most prevalent in cavities of volcanic basalt. Also in seams in diabase and Serpentine rock, and in nepheline syenite pegmatites.
Rock Type
Igneous, Metamorphic

Uses

Natrolite specimens are of interest to collectors, especially those specializing in zeolite minerals. Large individual crystals are particularly desirable among collectors. Transparent Natrolite crystals are occasionally faceted into rare gemstones for collectors. Natrolite as a zeolite is also used in water purifiers and chemical filters.

Noteworthy Localities

The largest crystals of Natrolite, as single floaters, were found in the Khibiny Massif, Kola Peninsula, Russia. These crystals were very scarce and are hard to come across; only a very limited supply of them was ever released from the find. In Australia, rounded spiky puffs come from Cape Grim, Tasmania. The Indian basalt deposits, known for their spectacular zeolite minerals, are surprisingly scarce in Natrolite. Although the related mineral Scolecite is fairly abundant in the state of Maharashtra, India, Natrolite has been found only sparingly, in the cities of Pune (Poona), Mumbai, and Nasik, mostly as elongated brittle sprays. In Europe, pink and brownish globular formations of Natrolite have come from the Ústí Region, Bohemia, Czech Republic. White slender crystal groups have come from Puy de Marmant, Puy de Dôme, France; and white and light pink needle sprays from Piz Sella, Bolzano Province, Italy.

In the U.S., the state of New Jersey is the most prolific producer of Natrolite, with several important deposits. Acicular groupings are abundant at the Upper New St. Quarry, Paterson, Passaic Co. Nearby Prospect Park, Passaic Co. has also produced nice acicular Natrolite, sometimes with pinkish tones. Very large crystals up to 10 cm., sometimes water-clear, have come from the Chimney Rock Quarry, Bound Brook, Somerset Co., New Jersey. Snow-white crystal groupings and acicular balls in very aesthetic formation were once prevalent at the Millington Quarry, Somerset Co., New Jersey.

Natrolite is a white massive matrix of micro-crystals for the rare minerals Benitoite and Neptunite at the Dallas Mine, San Benito Co., California. Natrolite has also occurred there as a single gemmy elongated crystals in occasional finds. Hemispherical Natrolite balls are well-known from the Horseshoe Dam area, Maricopa Co., Arizona. In Canada, water-clear, flawless crystals were found at Mont Saint Hilaire, Quebec, as well in white crystals and groups associated with Serandite. In Nova Scotia, Natrolite can be found at Wasson's Bluff in Parrsboro, and at the Five Islands area.

Common Mineral Associations

Calcite, Prehnite, Analcime, Apophyllite, Stilbite, Laumontite, Datolite

Distingushing Similar Minerals

Mesolite - Usually in thinner crystal, otherwise very difficult to distinguish.
Scolecite - Usually in thicker crystals, or in columnar or reticulated groupings, otherwise very difficult to distinguish.
Pectolite - Usually more fibrous, and rarely has the individual crystals in radial and aciular groupings as does Natrolite.
Acicular Gypsum - Much softer, different crystal form.


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