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Chemical context

Calcium Amphibole Subgroup

mindat.org

March 13, 2023A_nCa₂(Z²⁺_5-mZ³⁺_m)(Si_8-(n+m)Al_(n+m))(OH,F,Cl)₂The calcium amphibole subgroup is one of the subgroups belonging to the W(OH,F,Cl)amphibole group. It is defined by Ca>1,5 apfu in the X position (= IMA B position). The calcium amphibole subgroup are further divided into root-name groups that are defined by the value of n and m (edenite and tschermakite substitutions) in the generic formula above. The generic formula does not apply fully to root-name groups or species containing elements with other valence values than standard. The various positions in the formula can have the following content: A position: x=0 or 1, when 1, it normally contains a single valence element,most often Na or K but also Ca or Pb. Z²⁺ position (= IMA C²⁺ position): m may be 0,1 or 2. The Z²⁺ positions normally contains Mg or Fe as the dominant elements. Z³⁺ position (= IMA C³⁺ position): Normally contains Al or Fe, but also Cr or Ti are known as the dominant elements in this position. On mindat.org we avoid using variables with the same symbol as elements and deviate from the IMA nomenclaure in that we use X rather than B, Z rather than C and (OH,F,Cl,O) rather than W.

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