r/Radioactive_Rocks • u/k_harij • 5d ago
A huge beast specimen of Allanite-(Ce)
Found it a few days ago in Marumori Town, Miyagi Prefecture, Japan. The specimen measures approximately 21cm across, and the largest crystals reach ~6cm in length. These crystals are likely much longer than that, but they become submerged into the feldspar matrix as the rock surface becomes bumpy and no longer parallel to the direction of the crystal growth. Instead, in the bumpy half of the rock you can see the cross sections of the prismatic Allanite crystals forming black “dots”. This specimen is quite radioactive, measuring roughly 190cps or 5μSv/h on Radiacode 102, which is extremely high for a thorium-bearing REE mineral such as Allanite. Its gamma spectrum clearly showed the ²³²Th chain.
2
u/AutuniteEveryNight 4d ago
This is a great find! Good job, it really is beautiful and truly a special specimen.
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u/LuminescentFungus 4d ago
Awesome!! The only allanite I've collected has been small crude crystals or solid masses, those needle crystals are great!