Macusanite Identification Guide

What Macusanite Looks Like

Macusanite is a rare natural volcanic glass (a peraluminous obsidian, sometimes called a tektite-like glass) from the Macusani region of Peru. It is prized for being unusually pale and gem-quality compared to typical black obsidian.

• Color: pale greenish-yellow, smoky tan, to nearly colorless; often translucent
• Luster: vitreous (glassy)
• Transparency: translucent to nearly transparent — much clearer than ordinary obsidian
• Habit: amorphous glass; rounded nodules and fragments with conchoidal fracture

Step-by-Step Field ID Checklist

1. Note the pale, translucent color — this is not black obsidian; macusanite is light greenish-yellow and lets light through.
2. Look for conchoidal fracture — smooth, shell-like curved breaks with razor edges.
3. Test hardness — about 5.5-6, scratches glass marginally and is scratched by quartz.
4. Heft it — natural glass is light (SG ~2.3-2.4), lower than most crystalline gems.
5. Inspect for flow bands or tiny inclusions/bubbles typical of natural glass.

Key Diagnostic Tests

• Mohs hardness: ~5.5-6.
• Streak: white.
• Fracture: conchoidal, no cleavage.
• Specific gravity: ~2.3-2.45, low.
• Optics: isotropic (singly refractive) — like all glass.

Common Look-Alikes and How to Tell Them Apart

• Moldavite (a tektite): green and also glassy/isotropic, but moldavite is bottle-green with sculpted etched surfaces; macusanite is paler and more yellow-green.
• Ordinary obsidian: usually black/opaque; macusanite is pale and translucent.
• Volcanic/man-made glass slag: look for bright artificial colors and abundant bubbles; macusanite's color is muted and natural.
• Pale chalcedony: harder (7), microcrystalline, no glassy conchoidal sheen of true glass.

Where It Is Typically Found

Macusanite is found almost exclusively around Macusani, in the Puno region of southeastern Peru, weathering out of a peraluminous rhyolitic volcanic field as small nodules and pebbles.