Spectrolite Identification Guide

What Spectrolite Looks Like

Spectrolite is a trade name for a premium grade of labradorite (a calcium-rich plagioclase feldspar) originally from Ylämaa, Finland. The base body color is dark gray to nearly black, but when light strikes it at the right angle it flashes a broad spectrum of color — blue, green, gold, orange, violet and even red — often all in one stone. This optical play, called labradorescence, comes from light scattering off microscopic lamellar twinning planes inside the feldspar.

• Luster: subvitreous to slightly silky on flash; dull on broken matrix
• Transparency: opaque to translucent
• Habit: anhedral cleavable masses; the flash appears as broad sheets, not pinpoints

Step-by-Step Field-ID Checklist

1. Rock the stone under a single light source. Genuine spectrolite shows a metallic-looking sheen that ignites and dies as you tilt it — it is directional, not a surface coating.
2. Look at the color range. Ordinary labradorite usually flashes only blue or blue-green. True spectrolite shows multiple colors including the rare reds and purples.
3. Find a broken edge or cleavage face. Feldspar shows two cleavage directions meeting at nearly 90°, giving stepped, blocky surfaces.
4. Check the body color. Spectrolite is characteristically dark gray-black, which makes the flash more vivid by contrast.

Key Diagnostic Tests

• Mohs hardness: 6–6.5. It will scratch glass but a steel file will scratch it.
• Streak: white.
• Cleavage: two good cleavages at ~86°/94° (typical of plagioclase) — look for the flat, mirror-like step faces.
• Fracture: uneven to conchoidal where it crosses cleavage.
• Density: ~2.68–2.72 g/cm³, feels moderate in the hand.
• No magnetism, no acid reaction.

Common Look-Alikes and How to Tell Them Apart

• Ordinary labradorite: chemically identical; spectrolite is simply the top grade with full-spectrum, high-contrast flash on a black base. The distinction is quality, not species.
• Larvikite ("black moonstone"/blue granite): a syenite rock with blue-silver schiller in blocky feldspar grains, but it is a granular rock with multiple minerals, not a single cleavable mass, and the sheen is steely blue-gray rather than rainbow.
• Rainbow moonstone (white labradorite): translucent and pale with a blue adularescent sheen — light body color versus spectrolite's dark base.
• Andesine/sunstone: sunstone shows coppery aventurescent sparkle (platelet inclusions), not broad sheet labradorescence.
• Dyed or coated imitations: an even, all-over iridescence that does not shift directionally, or color seen on the surface from every angle, signals a coating.

Where It Is Found

Classic spectrolite comes from Ylämaa, southeastern Finland, hosted in anorthositic intrusions. Labradorite of spectrolite quality is rare; most labradorite worldwide (Madagascar, Canada's Labrador, Ukraine) flashes fewer colors. Look for it in anorthosite and gabbroic rocks.