Macusanite
Peraluminous rhyolitic volcanic glass
A rare translucent yellow-green volcanic glass from the Macusani region of Peru, valued by faceters and sometimes confused with tektites.
- Mohs hardness
- 5.5-6
- Color
- Pale yellow-green to olive, translucent
- Type
- igneous
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Overview
Macusanite is a natural volcanic glass found near Macusani in southeastern Peru. It is a peraluminous (aluminum-rich) rhyolitic glass, typically pale yellow-green and translucent, and is sometimes loosely called "Macusani obsidian."
Because of its translucency and clean color it is often cut as a faceted collector gem. It has occasionally been mislabeled a tektite, but it is a terrestrial volcanic glass, not an impact glass — although its unusual lithium- and boron-rich chemistry has made it a subject of scientific study.
It is comparatively rare and prized by gem and meteorite collectors alike for its softly glowing color.
Formation & geology
Macusanite formed from highly evolved, water- and lithium-rich rhyolitic magmas erupted in the Macusani volcanic field of the Peruvian Andes during the Neogene. Rapid cooling of this peraluminous melt produced glass instead of a fully crystalline rock.
The glass is enriched in lithium, boron, fluorine, and other incompatible elements, reflecting an extremely fractionated source magma associated with the region's tin and uranium mineralization.
Specimens are recovered as small water-worn pebbles and fragments weathered out of tuffs and ignimbrites in the high Andean terrain around Macusani, Puno Department.
How to identify it
Look for small translucent pebbles of pale olive to yellow-green glass with a vitreous luster and conchoidal fracture. Hardness is about 5.5-6 and streak is white.
When held to light it transmits a soft green glow, unlike most ordinary black obsidian. It can resemble moldavite or other tektites, but macusanite is generally a paler, more uniform yellow-green and comes specifically from Peru.
Distinguish from green bottle glass (which is artificial and often has bubbles in regular rows or mold seams) and from peridot or green tourmaline, which are crystalline and harder. Genuine macusanite is a natural amorphous glass.
Uses & significance
Macusanite is chiefly a collector and gem material: it is faceted into translucent green gemstones and kept as a curiosity by meteorite and tektite enthusiasts despite being volcanic in origin.
Scientifically it is important as a natural example of peraluminous, lithium-boron-rich glass and has been used in geochemical and experimental petrology studies.
It has no major industrial use and only minor metaphysical following, where it is associated, like other green glasses, with transformation.
Frequently asked questions
Is macusanite a tektite?
No. Despite sometimes being sold alongside tektites, macusanite is a terrestrial rhyolitic volcanic glass from Peru, not an impact-melt glass.
Where does macusanite come from?
It comes from the Macusani volcanic field near Macusani in the Puno region of southeastern Peru.
Why is macusanite green?
Its pale yellow-green color comes from its specific glass chemistry, including iron and other trace elements, in a translucent rhyolitic glass.
Can macusanite be faceted?
Yes. Its translucency and clean color make it a popular material for faceted collector gems, though it is relatively soft for daily-wear jewelry.
Macusanite guides
In-depth guides for identifying, valuing, and understanding Macusanite.
