Analcime is a popular and interesting mineral. It is sometimes known
as analcite, although analcime is preferred. It is one of the few minerals
that characteristically forms its own unique crystal. Well, not quite its
own unique crystal, but pretty close. It forms the isometric trapezohedron.
The minerals of the garnet
group and high temperature leucite
are the only common minerals that will also form the trapezohedron. The
trapezohedron has 24 deltoid-shaped faces, where each face occupies one
third of the position of a single octahedron's face.
Distinguishing analcime from the garnets and leucite is relatively easy
in some cases. The garnets are much harder and usually deeply colored.
Leucite has a much lower density and usually has a dull luster. Also leucite
is typically embedded in host rock where as analcime, when displaying good
crystals and not massive or granular, is loose or attacted to other minerals
in volcanic cavities.
is actually distantly related to leucite, KAlSi2O6.
Leucite is a member of the feldspathoid
group of minerals. Minerals whose chemistries are close to that of
the alkali feldspars
but are poor in silica (SiO2) content, are called
feldspathoids. Feldspathoids are commonly found in silica-poor igneous
rocks, where analcime is sometimes present as well. Analcime is sometimes
placed in the feldspathoid group since its chemistry and occassional occurrences
Analcime's structure however has a typical zeolite openness about it
that allows large ions and molecules to reside and actually move around
inside the overall framework. The structure contains large open channels
that allow water and large ions to travel into and out of the crystal structure.
The size of these channels controls the size of the molecules or ions, and
therefore a zeolite like analcime can act as a chemical sieve.
Color is clear, white or gray, with greenish, yellowish and
reddish tints possible.
Luster is vitreous.
Transparency: crystals are transparent to translucent.
Crystal System is isometric; 4/m bar 3 2/m
Crystal Habits include the characteristic trapezohedron as well
as the rare cube modified by trapezohedral faces. Also granular and massive.
Cleavage is absent.
Fracture is uneven.
Hardness is 5 - 5.5.
Specific Gravity is approximately 3.2 (average)
Streak is white.
Associated Minerals are quartz,
and other zeolites.
Notable Occurrences include Mont St. Hilaire, Quebec; Iceland;
several localities in Oregon, Colorado and New Jersey, USA; Nova Scotia
Best Field Indicators are crystal habit, density, low hardness,
luster and associations.