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What to look for

Under 10x loupe: fan-shaped or radiating bundles of pale yellowish fibers all emerging from a single dark central point. The fibers curve outward, like a horse's tail.

What it means

Horsetail inclusions are strongly associated with Russian demantoid and are composed of byssolite or related fibrous amphibole minerals. They are an important species and origin clue.

Expert move

These inclusions are so prized they can increase value rather than reduce it. Namibian demantoid usually shows different inclusion features such as chromite crystals.

Gemstone inclusion

Horsetail Inclusions

Under 10x loupe: fan-shaped or radiating bundles of pale yellowish fibers all emerging from a single dark central point. The fibers curve outward, like a horse's tail.

Category Needles

Seen in

Demantoid Garnet strongly associated with Russian demantoid (Ural Mountains); can occur rarely in demantoid from Namibia Italy but is rarest most prized in Russian material

Check with

10x loupe visible even at low magnification

Reading order

Confirm the feature is internal, not surface dirt or polish marks.
Use side light to reveal relief, planes and shimmer.
Compare with related stones before making an origin or treatment call.