Canasite

Canasite
General
Category	Mineral
Formula (repeating unit)	K3Na3Ca5Si12O30(OH)4
IMA symbol	Cns[1]
Strunz classification	09.DG.80
Dana classification	78.05.04.01
Crystal system	Monoclinic
Crystal class	Monoclinic-Prismatic
Unit cell	1,596.05
Identification
Color	Brownish Yellow, Green Yellow, Light Green
Twinning	Polysynthetic
Cleavage	Perfect 1 direction, good 1 direction
Fracture	Splintery
Mohs scale hardness	5 - 6
Luster	Vitreous
Streak	White, Clear
Diaphaneity	Transparent, translucent
Specific gravity	2.707
Density	2.707
Optical properties	Biaxial (-)
Refractive index	nα = 1.534 nβ = 1.538 nγ = 1.543
Birefringence	0.009
Pleochroism	None
2V angle	Measured 58° Calculated 84°
Dispersion	Weak r > v
Fusibility	Easily fusible to a transparent glass
Solubility	Readily decomposed by acids
Other characteristics	Radioactive 1.12% (K)
Major varieties
Fluorcanasite	K3Na3Ca5Si12O30F4 · H2O
Frankamenite	K3Na3Ca5(Si12O30)[F,(OH)]4·(H2O)

Canasite is a mineral whose name is derived from its chemical composition of calcium (Ca), sodium (Na), and silicon (Si).^[2] It was approved in 1959 by IMA.

It is a relatively rare mineral. It occurs as aggregates in charoite, creating cabochons when contrasted against swirling purple charoite. It is extremely rare for canasite to be faceted. As crystals, it occurs in a size up to 10 cms, but in platy aggregates it can reach up to 20 cms in size. It is also granular.^[3] Twinning is usual, and can occur as polysynthetic, which is when multiple twins align in a parallel.^[4] It has a barely detectable 1.12% potassium radioactivity based on the GRapi unit (Gamma Ray American Petroleum Institute Units).^[5] It consists of mostly oxygen (41.98%), silicon (26.8%) and calcium (15.93%), but otherwise contains sodium (7.31%), potassium (6.22%), which gives its radioactive properties, fluorine (1.51%) and hydrogen (0.24%).^[4] There are two varieties of canasite: fluorcanasite and frankamenite. Purple canasite may be confused with stichtite, but recent research has found that the mineral advertized as canasite is a new specimen.^[6]

Canasite has been found in three localities, all in Russia. In Khibiny massif, it grows in a differentiated alkalic massif in pegmatites, and in the Murun massif, it grows in charoitic rocks. It also occurs in the Kola Peninsula. In Khibiny massif, it is associated with titanite, eudialyte, orthoclase, nepheline, pyroxene, lamprophyllite and fenaksite, while the specimens from Murun massif are usually associated with charoite, tinaksite and miserite.^[2]