Fluorite from China, Fujian, Yunxiao Co., Tongbei, Wushan Spessartine Mine

Another species in my locality (Tongbei) collection. This features a nice contrast between large octahedron purple fluorite and light-color, secondary hyalite opal coating granite matrix, probably mined 15-20 years ago. Large euhedral fluorite crystals are rarely seen in magmatic origin especially for A-type granite, the project I am working on, due to the low calcium content in the late stage of magmatism because crystallization of plagioclase +- amphibol consumed most of Ca.

The color zoning is also interesting, doesn't like Others that zonation formed as muti-stages of recrystallization with different content of Color inducing elements along the crystallographic edges. If you look closer, you will notice that the dominant color is actually colorless the overall deep purple and blue tones are generated by internal diffuse reflection of dark color zonations.

Fluorite and topaz are important fluorine-bearing minerals in silisic magam. Why they are usually found in intraplate extension setting rather than continent arc which is a very interesting question. Fluorin content probably the first role. Over a large range of added H2O (∼1–7 wt%), melts containing <1 wt% F precipitated titanite without fluorite, whereas melts containing >1 wt% F precipitated fluorite without titanite. Topaz is probably both aluminum and volatile controlled that occurs when excess aluminum in the melt. I was lucky to find this one for my collection 2 years ago.

Fluorite, spessartine,quartz, 7 cm, Tongbei, Yunxiao County, Zhangzhou, Fujian, China.

Jingnan Zhang Coll, Jeff Scovil photo.