Alforsite

alforsite

sanbornite

witherite

gillespite

Images

Formula: Ba5(PO4)3Cl
Anhydrous phosphate containing halogen, apatite group, apatite supergroup, barium-bearing mineral
Crystal System: Hexagpnal
Specific gravity: 4.80 calculated
Hardness: 5
Streak: White
Colour: Colourless
Luminescence: Not fluorescent under UV, but intense violet cathodluminescence in 10 to 15 kV electron beam
Environments

Sedimentary environments
Metamorphic environments

Alforsite occurs in lenses and bands of barium silicate metasediments developed under hornblende-pyroxene hornfels facies rocks near the contact with granite or granodiorite. Associated minerals include celsian, witherite, sanbornite, gillespite, fresnoite, fluorapatite, walstromite, titantaramellite, quartz, tourmaline and pyrite (HOM).

Localities

There are two co-type localities, Big Creek and the Esquire No. 7 claim, Big Creek, both at the Big Creek-Rush Creek Mining District, Fresno county, California, USA.

In the Big Creek-Rush Creek Mining District, Fresno county, California, USA, alforsite occurs as .05 mm or smaller grains disseminated in fine-grained metamorphic sanbornite-quartz rock. The alforsite-bearing samples are massive grey rocks with gneissic banding due primarily to segregations of quartz. The samples from Big Creek which contain alforsite are lighter grey than those from Incline. They are quartz-rich and contain no gillespite. The alforsite and fluorapatite are scattered within different fine-grained bands which contain a high proportion of quartz and alternate with bands bearing quartz in lesser amounts. Both bands contain abundant celsian, witherite and sanbornite with accessory, disseminated fresnoite, walstromite, tourmaline and pyrite. Nearly pure fluorapatite is also common in these samples. The two apatite group members (fluorapatite and alforsite) have not been found touching one another in thin section and are generally in different bands in the rocks. Apatites typically form complete solid solutions between end-members. Alforsite occurs in an assemblage of sanbornite, quartz and witherite (AM 66.1050-1053).

At Incline, Clearing House Mining District, East Belt, Mariposa county, California, USA, alforsite occurs as .05 mm or smaller grains disseminated in fine-grained metamorphic sanbornite-quartz rock. The alforsite-bearing samples are massive grey rocks with gneissic banding due primarily to segregations of quartz. Prominent bands of pink gillespite occur and here alforsite is associated with sanbornite, witherite and celsian in quartz-rich and gillespite-rich bands. Fresnoite, walstromite, tourmaline and pyrite, though less abundant, are disseminated throughout the rock (AM 66.1050-1053).

Back to Minerals