Eucryptite is a lithium bearing aluminium silicate mineral with formula LiAlSiO4.

It typically occurs as granular to massive in form and may pseudomorphically replace spodumene.

It is transparent to translucent and varies from colorless to white to brown.

Optically it is uniaxial positive with refractive index values of nω = 1.570 – 1.573 and nε = 1.583 – 1.587.

Its typical occurrence is in lithium-rich pegmatites in association with albite, spodumene, petalite, amblygonite, lepidolite and quartz.