Rainbow Andradite Garnet – Tenkawa, Nara Prefecture, Japan
This striking specimen is composed of tightly packed, highly lustrous dodecahedral garnet crystals that exhibit a vibrant surface iridescence. Commonly referred to as “Rainbow Garnet,” this optical effect is caused by diffraction at extremely thin lamellar layers within the garnet crystal structure. These layers act like a natural diffraction grating, splitting white light into its spectral colors and producing a metallic rainbow sheen—particularly when viewed at specific angles.
Mineralogically, these garnets are members of the andradite subgroup within the garnet family, rich in calcium and iron. While andradite itself is not uncommon, the rainbow variety from Japan is exceptionally rare and was long known only to a few collectors due to limited access and highly localized production.
The most famous and well-documented deposits are located in the mountainous forests of Tenkawa in Nara Prefecture. Discovered in the late 20th century, these deposits have produced relatively small but intensely colorful specimens. Collecting is now heavily restricted or prohibited, making existing specimens increasingly valuable on the market.
This piece is a classic example—showcasing the tight cluster of sharp crystal faces and the unmistakable iridescence that has earned Rainbow Garnet its place among the world’s most unique collector garnets. The host rock is weathered rhyolite or a similar felsic volcanic rock
24.6 x 22.1 x 18.2 mm
Estimate: $225 - $235
