Peristerite Identification Guide
Recognizing peristerite, a feldspar that shows a blue-white pigeon-neck schiller, and distinguishing it from moonstone and labradorite.
Read the full Peristerite encyclopedia entry →
What Peristerite Looks Like
Peristerite is a variety of sodium-rich plagioclase feldspar (albite–oligoclase) that displays a soft blue to blue-white sheen called peristerism — named for the iridescence on a pigeon's neck. The body color is usually milky white, pale gray, or cream, and the floating blue glow appears when light hits microscopic intergrowth lamellae at the right angle. It is transparent to translucent with a vitreous to slightly pearly luster, and typically occurs as cleavable masses or grains rather than well-formed crystals.
Step-by-Step Field ID Checklist
- Tilt for the sheen. Rotate the stone under a single light source and watch for a blue to silvery-blue glow that moves across the surface.
- Note the body color. A white-to-gray feldspar base with blue (not multicolor) flash is the signature.
- Find cleavage planes. Look for two flat, shiny cleavage directions meeting near 90°, typical of feldspar.
- Test hardness. It scratches glass (Mohs 6–6.5) but not as easily as quartz.
- Rule out rainbow colors. If you see greens, golds, and reds, it is more likely labradorite, not peristerite.
Key Diagnostic Tests
- Hardness: 6–6.5; scratches glass.
- Streak: White.
- Cleavage: Two good cleavages at ~94°, with stepped, blocky breaks.
- Luster: Vitreous to pearly on cleavage faces.
- Density: ~2.62, light for its size.
- Acid/magnetism: No reaction; not magnetic.
Common Look-Alikes and How to Tell Them Apart
- Moonstone (orthoclase/adularia): Shows a billowy white-to-blue adularescence that seems to float inside the stone, whereas peristerite's blue sheen sits more on the surface; moonstone is potassium feldspar.
- Labradorite: Displays bold multicolor labradorescence (blue, green, gold, copper), not just clean blue; labradorite is calcium-richer plagioclase.
- Rainbow moonstone: Actually a labradorite; broader color range than peristerite.
- Blue chalcedony: Has the blue color in the body itself, no directional sheen, and is harder (7) with no cleavage.
- Opal: Plays multiple spectral colors and is softer with no cleavage.
The combination of feldspar cleavage plus a pure blue (not multicolor) schiller pins down peristerite.
Where Peristerite Is Found
Peristerite occurs in pegmatites and metamorphic gneisses where sodic plagioclase has unmixed on cooling. Well-known sources include Ontario and Quebec in Canada (the classic localities), plus Norway, Tanzania, and parts of the United States. Search granitic pegmatite dumps and feldspar quarries.
Frequently asked questions
How can you tell if it's real peristerite?
Genuine peristerite is a feldspar showing a clean blue to blue-white sheen, has two cleavage directions near 90°, scratches glass at hardness 6–6.5, and lacks the multicolor flashes of labradorite.
Peristerite vs moonstone — what's the difference?
Moonstone is potassium feldspar with a soft floating adularescence, while peristerite is sodic plagioclase whose blue schiller sits closer to the surface; chemistry and the look of the glow differ.
Why does peristerite glow blue?
The blue sheen, called peristerism, comes from light scattering off submicroscopic albite–oligoclase intergrowth lamellae that formed as the feldspar slowly unmixed during cooling.
Is peristerite the same as labradorite?
No. Both are plagioclase feldspars, but labradorite shows broad multicolor labradorescence, whereas peristerite shows a narrower, predominantly blue iridescence.
What color is peristerite?
Its body is typically milky white, pale gray, or cream, overlaid by a moving blue to silvery-blue schiller that appears as you tilt the stone toward a light.