Achroite

Achroite is the rare colorless variety of tourmaline, belonging to the lithium-rich species elbaite. Its name comes from the Greek achroos, meaning "without color," describing its near-total lack of pigment.

Colorless tourmaline is uncommon because most tourmaline contains trace elements that impart color. Truly colorless stones are scarce; many "achroite" stones show a faint pink, blue, or greenish tint.

Achroite forms the same striated trigonal prisms as other tourmalines and is sometimes found at the colorless end of color-zoned crystals.

Achroite forms in granitic pegmatites, the same lithium- and boron-rich environment that produces colorful elbaite. The colorless result occurs when the crystal grows nearly free of the chromophore trace elements (manganese, iron, copper) that give other tourmalines their color.

It often appears as a color zone, for example the clear band in some watermelon or zoned crystals, rather than as a fully colorless crystal. Notable sources include Madagascar, Brazil, the USA (California, Maine), and Pakistan.

Resistant crystals may also be recovered from alluvial gem gravels.

Look for a colorless, transparent crystal or cut stone with a rounded triangular cross-section and lengthwise striations, the tourmaline signatures. Hardness is 7-7.5, luster vitreous, streak white.

Even though it is colorless, achroite still shows double refraction (birefringence), which helps separate it from singly refractive colorless stones like diamond, spinel, and garnet. Its lower hardness and refractive index distinguish it from colorless sapphire and diamond.

Distinguish from colorless quartz and topaz by crystal form, birefringence strength, and lack of cleavage (topaz has perfect cleavage).

Achroite is a collector's gemstone, faceted to show its clarity and brilliance. Because colorless tourmaline is rare, fine examples are valued more as curiosities and completist pieces than as mainstream jewelry stones.

It is occasionally used as an accent or in unusual designs that highlight its transparency. Its hardness makes it durable enough for everyday wear.

Metaphysically, colorless tourmaline is associated with clarity and balancing the other tourmaline colors, though such claims are not scientifically supported.