15 cm wide andradite/hedenbergite step with a green apatite stem, behind it apophyllite.

Step and photo: Jürgen Tron.

Beautiful, freely crystallized apatites are known worldwide from extremely diverse occurrences, such as pegmatite geodes, tin veins, and alpine-type fissures (→“Profile” in Lapis 12/2005). Skarns, however, rarely yield collectible material, and until now, freestanding crystals in garnet geodes had never been observed in such occurrences. This changed last autumn.
In mid-September 2020, a geode was opened in the Shijiangshan skarn deposit in Chinese Mongolia, world-famous for its rare borates (→Lapis 11/2018). Around 30 specimens of reddish-black garnet crystals were unearthed, a dozen of which also contained green fluorapatite. The material was sent to Jürgen Tron (Stegaurach), who informed the Lapis editorial team about the find in November and sent several photos upon request.
The conclusion: Apatite is new to this location, and its freestanding combination with skarn garnet is probably unique worldwide. The pieces, some measuring over 15 cm, reveal the following mineral sequence: garnet (probably andradite), pyroxene (hedenbergite?), fluorapatite, iron-rich axinite, and apophyllite.
The transparent apatite prisms reach up to 2 cm in length, while the garnet rhombic dodecahedra even attain a diameter of 4.5 cm. Apatite likely formed during the last hydrothermal phase in the skarn. As Berthold Ottens already noted (Lapis 11/2018), the borate-bearing skarns of the Shijiangshan/Shalonggou district differ significantly from those in the Huanggang district (Lapis 4/2012 + 10/2013), where iron arsenides, beryllium, and fluorine are more concentrated; the typical sequence of arsenopyrite/löllingite, helvine/genthelvine, and fluorite formed there.
Many thanks to Jürgen Tron [www.tron-xx.eu] for the information and photos!
Stefan Weiß.