mineral

Star Sapphire

Corundum (Al2O3) with Rutile inclusions

Hardness: 9 on Mohs scale; Color: Blue, purple, or greyish-blue; Luster: Vitreous; Crystal Structure: Trigonal; Asterism: Features a six-rayed star effect caused by light reflecting off microscopic rutile needles (silk).

Hardness: 9 on Mohs scale
Color: Blue, purple, or greyish-blue
Luster: Vitreous

Identified March 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed in aluminum-rich metamorphic rocks (gneiss/schist) or igneous rocks (alkaline basalts). The asterism develops during the cooling process when titanium-rich rutile crystallizes inside the sapphire host.

Uses & applications

Primary use is in high-end jewelry as cabochons. It is also a highly sought-after specimen for gemstone collectors.

Geological facts

The 'star' effect is called asterism. The most famous example is the 'Star of India,' weighing 563 carats. High-quality star sapphires are very rare because they must contain exactly the right amount of silk to show a star without ruining the transparency.

Field identification & locations

Identify by shining a single point of light on the dome (cabochon); the star should glide across the surface as the light moves. Commonly found in Sri Lanka (Ceylon), Myanmar (Burma), and Thailand.

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