Eucryptite
Encyclopedia
Eucryptite is a lithium
bearing aluminium silicate mineral
with formula LiAlSiO4. It crystallizes in the trigonal - rhombohedral crystal system
. It typically occurs as granular to massive in form and may pseudomorph
ically replace spodumene. It has a brittle to conchoidal fracture and indistinct cleavage. It is transparent to translucent and varies from colorless to white to brown. It has a Mohs hardness of 6.5 and a specific gravity of 2.67. Optically it is uniaxial positive with refractive index
values of nω = 1.570 - 1.573 and nε = 1.583 - 1.587.
Its typical occurrence is in lithium-rich pegmatite
s in association with albite
, spodumene
, petalite
, amblygonite
, lepidolite
and quartz
.
It occurs as a secondary alteration product of spodumene
. It was first described in 1880 for an occurrence at its type locality
, Branchville, Connecticut
. Its name was from the Greek
for well concealed, for its typical occurrence embedded in albite.
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
bearing aluminium silicate mineral
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
with formula LiAlSiO4. It crystallizes in the trigonal - rhombohedral crystal system
Crystal system
In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals...
. It typically occurs as granular to massive in form and may pseudomorph
Pseudomorph
In mineralogy, a pseudomorph is a mineral or mineral compound that appears in an atypical form , resulting from a substitution process in which the appearance and dimensions remain constant, but the original mineral is replaced by another...
ically replace spodumene. It has a brittle to conchoidal fracture and indistinct cleavage. It is transparent to translucent and varies from colorless to white to brown. It has a Mohs hardness of 6.5 and a specific gravity of 2.67. Optically it is uniaxial positive with refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
values of nω = 1.570 - 1.573 and nε = 1.583 - 1.587.
Its typical occurrence is in lithium-rich pegmatite
Pegmatite
A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....
s in association with albite
Albite
Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. As such it represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi3O8. It is a tectosilicate. Its color is usually pure white, hence...
, spodumene
Spodumene
Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, LiAl2, and is a source of lithium. It occurs as colorless to yellowish, purplish, or lilac kunzite , yellowish-green or emerald-green hiddenite, prismatic crystals, often of great size...
, petalite
Petalite
Petalite, also known as castorite, is a lithium aluminium tectosilicate mineral LiAlSi4O10, crystallizing in the monoclinic system. Petalite is a member of the feldspathoid group. It occurs as colorless, grey, yellow, yellow grey, to white tabular crystals and columnar masses. Occurs in...
, amblygonite
Amblygonite
Amblygonite is a fluorophosphate mineral, AlPO4, composed of lithium, sodium, aluminium, phosphate, fluoride and hydroxide. The mineral occurs in pegmatite deposits and is easily mistaken for albite and other feldspars. Its density, cleavage and flame test for lithium are diagnostic. Amblygonite...
, lepidolite
Lepidolite
Lepidolite Lepidolite Lepidolite (KLi2Al(Al,Si)3O10(F,OH)2 is a lilac-gray or rose-colored phyllosilicate mineral of the mica group that is a secondary source of lithium. It is associated with other lithium-bearing minerals like spodumene in pegmatite bodies. It is one of the major sources of the...
and quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
.
It occurs as a secondary alteration product of spodumene
Spodumene
Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate, LiAl2, and is a source of lithium. It occurs as colorless to yellowish, purplish, or lilac kunzite , yellowish-green or emerald-green hiddenite, prismatic crystals, often of great size...
. It was first described in 1880 for an occurrence at its type locality
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
, Branchville, Connecticut
Branchville, Connecticut
Branchville is a section of the southeast corner of the Town of Ridgefield, Connecticut, and is also the name of a Metro North railroad station .- History :...
. Its name was from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
for well concealed, for its typical occurrence embedded in albite.