Natural Iris Agate 15.4ct Teardrop Cabochon

Photographed on its edge to showcase the stone's defining quality, this teardrop cabochon delivers a full-spectrum rainbow display. The body is warm golden amber with tightly packed concentric banding running through it, and when light hits at the right angle the bands diffract it into vivid spectral colours - cyan, green, yellow, orange, and red arc visibly across the upper portion in a single bright band. The stone is semi-transparent and thin at 3mm, which is precisely the condition that produces the iris effect: the closely spaced internal layers act like a diffraction grating. The pear silhouette is broad and well-proportioned at 33x23mm.

Iris agate is a variety of chalcedony in which extremely fine, tightly spaced growth bands diffract white light into its component colours, producing a rainbow-like display visible when the stone is held up to a light source at a suitable angle. This example is from Indonesia. The phenomenon is entirely natural and the stone is untreated. Iris agates are most effective when cut thin to maximise light transmission, and this piece at 3mm thickness sits in a very useful range. Well suited to a pendant setting where light can reach the stone from behind, or displayed flat with backlighting to show the full spectrum.

• Stone type: Iris agate
• Weight: 15.4ct
• Size: 33x23x3mm
• Color: Golden amber (with spectral iris display)
• Cut: Pear (teardrop) cabochon
• Clarity: Semi-transparent
• Treatment: Untreated
• Origin: Indonesia

Natural iris agate, rainbow-display chalcedony, sold loose.