Rock salt

Halite
Halite from the Wieliczka salt mine, Małopolskie, Poland
General
Category	Halide mineral
Formula (repeating unit)	NaCl
Strunz classification	3.AA.20
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Fm3m
Unit cell	a = 5.6404(1) Å; Z = 4
Identification
Formula mass	58.433 g/mol
Color	Colorless or white
Crystal habit	Predominantly cubes and in massive sedimentary beds, but also granular, fibrous and compact
Cleavage	Perfect {001}, three directions cubic
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	2.0 - 2.5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	2.17
Optical properties	Isotropic
Refractive index	n = 1.544
Solubility	Water-soluble
Other characteristics	Salty flavor, Fluorescent
References

Halite (pronunciation: /ˈhælaɪt/ or /ˈheɪlaɪt/), commonly known as rock salt, is a type of salt, the mineral form of sodium chloride (NaCl). Halite forms isometric crystals. The mineral is typically colorless or white, but may also be light blue, dark blue, purple, pink, red, orange, yellow or gray depending on the amount and type of impurities. It commonly occurs with other evaporite deposit minerals such as several of the sulfates, halides, and borates.

Halite occurs in vast beds of sedimentary evaporite minerals that result from the drying up of enclosed lakes, playas, and seas. Salt beds may be hundreds of meters thick and underlie broad areas. In the United States and Canada extensive underground beds extend from the Appalachian basin of western New York through parts of Ontario and under much of the Michigan Basin. Other deposits are in Ohio, Kansas, New Mexico, Nova Scotia and Saskatchewan. The Khewra salt mine is a massive deposit of halite near Islamabad, Pakistan. In the United Kingdom there are three mines; the largest of these is at Winsford in Cheshire producing on average a million tonnes per year.