sylvite

also syl·vine (-vēn') or syl·vin·ite (-vĭ-nīt')
n.
A colorless vitreous potassium chloride mineral, the major ore of potassium.

[Alteration of sylvine, from French, from New Latin (sal digestivus) Sylvii, (digestive salt) of Sylvius, probably after Franz de la Boë, or Franciscus Sylvius (1614-1672), German-born Dutch physician.]

Variant: sylvine

A mineral form of potassium chloride, KCl.

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Cubic -- hexoctahedral

Environment

Sedimentary salt beds, volcanic fumaroles.

Crystal description

Like halite, but the cubes are much more frequently modified by octahedron faces, which may even be dominant. Like halite, massive and cleavable.

Physical properties

Same as halite in color and luster, but not blue or purple. Hardness 2; specific gravity 2.0; fracture uneven; cleavage cubic. Brittle; transparent; water-soluble.

Composition

Potassium chloride (52.4% K, 47.6% Cl). Some Na may be present.

Tests

More bitter taste than halite. When sodium is not abundant the violet potassium flame is readily seen, but it may be masked by the sodium. More soluble than halite, it can be leached away from sea salt piles by rain.

Distinguishing characteristics

Distinguished from halite by the taste and the flame test. The crystals commonly show octahedral faces (rare in halite). In the mined occurrences, sylvite is frequently colored red by hematite inclusions, though there seems no genetic reason for it.

Occurrence

Sylvite forms layers like halite. Since it is more soluble than that mineral, sylvite beds will usually lie above the halite in the sedimentary deposit series; it is one of the closing minerals to come out of an evaporating salt lake. It is much rarer than halite. Good specimens come from Stassfurt, Germany, and from New Mexico.

Remarks

Both sylvite and halite are said to be very diathermanous, which means being transparent to heat waves; heat acts like light waves penetrating a transparent substance, passing easily through it without being absorbed and without warming the mineral itself. It is of economic importance as a major source of potash for fertilizer.

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The noun has one meaning:

Meaning #1: a mineral consisting of native potassium chloride; an important ore of potassium that is found in sedimentary beds
  Synonym: sylvine

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