Mineral Species: Scapolite

Chemical Formula: Na4(Al,Si)12O24Cl  to  Ca4(Si,Al)12O24(CO3,SO4) 

Chemical Name: Calcium Sodium Aluminum Silicate Carbonate Chloride Sulfate

Mineral Class: Tectosilicate Al-Si Framework

Mineral Notes: Scapolite is actually the name of a series between the sodium chloride rich Marialite and the calcium carbonate rich Meionite. The structure of scapolite is similar to feldspathoids in that it is composed of large open spaces in the framework of silicate and aluminium tetrahedrons. These open spaces are large enough to hold large ionic groups of either NaCl or CaCO3. The sulfate ion shown in the formula is typically barely more than a trace, but is found in far greater amounts than fluorine or hydroxide. Scapolite forms in metamorphic rocks from the alteration of plagioclase feldspars. The entire Scapolite series is analogous to the plagioclase series. Distinguishing Scapolite minerals from each other is difficult as they differ only slightly in density and refractive index, both increasing with rising calcium content. Scapolite has had a number of alternate names. Wernerite was the most common name but now it has mostly disappeared from use. Others include Mizzonite and Dipyre. The name comes from the Greek for "shaft", reflecting the stubby elongated prismatic crystals. These are tetragonal so that Scapolite commonly havs a square or octahedral cross-section. It belongs to a rather rare symmetry class that is shared by only two other well known minerals, Powellite and Scheelite. The symmetry class is the Tetragonal Dipyramidal Class and is characterized by only having the one primary four fold axis of rotation and a perpendicular mirror plane, denoted as 4/m. 

Description: A specimen of fused Scapolite crystals whose elongated form can easily be seen. The mineral has an attractive creamy colour and many crystal faces are very lustrous, throwing out many bright refections. Amongs the Scapolite crystals are small grains of black Schorl tourmaline. The pepper-like contrast is very attractive.

Location: Dobra Voda, Czech Republic.