Cancrinite


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cancrinite

[′kaŋ·krə‚nīt]
(mineralogy)
Na3CaAl3Si3O12CO3(OH)2 A feldspathoid tectosilicate occurring in hexagonal crystals in nepheline syenites, usually in compact or disseminated masses.

Cancrinite

 

(named after the Russian statesman E. F. Cancrin [Kankrin]), the group name of minerals representing a perfect isomorphic series of mixed crystals with the composition nNa6Ca2[AlSi04]6(C03)2⋅2—3H2O (carbonate cancrinite) + mNa6Ca2[AlSi04]6(S04)2⋅2—3H2O (sulfate cancrinite, or vishnevite). The Na:Ca ratio varies; often an impurity of K2O (up to 5 percent) is detected. Cancrinite belongs to the aluminosilicates, with a framework of hexagonal SiO4 rings and A1O4 tetrahedrons connected in vertical six-membered groups. In the ring cavities lie large ions of [SO4]2− or [CO3]2−, formingmolecular intrusive groups with the Ca or 2Na. The mineralcrystallizes in the hexagonal system (crystals are very rare);granular or fine-grained aggregates are common. Cancrinite iscolorless, gray, or pink; sometimes it is light blue (sulfate cancrinite). The prismatic cleavage is perfect. The mineral has a hardness of 5–5.5 on the mineralogical scale and a density of 2, 420–2, 500 kg/m3. In nature it forms from nepheline under the action of sulfate or carbonate postmagmatic solutions. It is found in nepheline syenites and other basic rocks as well as in alkaline pegmatites as a rock-forming mineral.

References in periodicals archive ?
This work included major element mineral chemistry for cancrinite, nepheline, and biotite from these rocks.
105) and is therein defined as "a coarse-grained, somewhat foliated variety of nepheline syenite consisting of K-feldspar, albite, nepheline, cancrinite, sodalite and lepiodomelane.
Cancrinite is anhedral, occurs in abundances of up to 10%, and shows no apparent textural affinity for other minerals.
As shown in Figure 5d, the transformation of kaolinite in NH,F solutions using SDA promoted the formation of sodalite and cancrinite.
Alteration of kaolinite to cancrinite and sodalite by simulated hanford tank waste and its impact on cesium retention.
Associated minerals are: potassium feldspar, sodalite, cancrinite, pectolite, aegirine, natrite, vililaumite, lomonosovite, chkalovite, nacaphite, fluorcaphite, vitusite, sphalerite and galena.
Furthermore, the similar species cancrinite, practically unknown heretofore in crystals, is present in one unique specimen as a fairly sharp, 2.
Surprisingly, only four members of the cancrinite group are found at Monte Somma/Vesuvius, although many others are known from similar volcanic rocks in Italy.
Afghanite is usually associated with sodalite-group minerals that are structurally related to the cancrinite group.
In order to understand why the cancrinite group has historically been so problematical for mineralogists it is necessary to understand something of the structural relationships.
While gathering samples for an extensive investigation of the cancrinite group we came across two intriguing specimens in the collection of the Mineralogical Museum of the University of Rome.
The first five of these, plus microsommite, davyne, afghanite and vishnevite, are all hexagonal and members of the cancrinite group.