Isomorphism in Vanadinite. 1. Chemical Variations and Solid Solutions

Using electron microprobe analysis (EMPA), the chemical composition of 100 vanadinite specimens from 17 occurrences is studied and new and published data on its chemical composition are summarized. Vanadinite is a supergene mineral: there are no reliable data that this chlorovanadate can be hypogene in origin, although its analog is synthesized in a wide temperature range from 25 to 1000°C. Most vanadinite specimens have almost ideal composition of Pb5(VO4)3Cl. Vanadinite rich in P and/or As (>0.5 apfu P or/and As), is rare, as is Cr-bearing vanadinite. According to available data, isomorphism between V, As, and P in natural vanadinite–pyromorphite–mimetite system is incomplete in contrast to the synthetic Pb5(T5+O4)3Cl (T = V, P, As) system with full miscibility (even at low temperatures). Composition of the vanadinite–mimetite series ranges from V3.00As0.00 to As2.15V0.85, whereas the vanadinite–pyromorphite series still has only vanadinite part from V3.00P0.00 to P1.50V1.50. Two new findings of so-called “endlichite” (an intermediate member of the vanadinite–mimetite series with a V : As ratio of ∼1 : 1) are described; previous chemical analyses of this mineral were published in 1885. The Ca content in all studied vanadinite specimens in this work does not exceed 0.2 apfu, whereas the content of other elements with atomic numbers of >8, except for Pb, Ca, V, P, As, and Cl, is below the EMPA detection limit.