Chevron Amethyst

Chevron amethyst grows in hydrothermal cavities and vein systems where silica-rich fluids cycle through fractures in host rock, most often granite, basalt, or altered metamorphic terrain. As the fluid cools and loses pressure, silicon and oxygen precipitate onto the cavity walls as quartz. Two chemical conditions alternate during this process. When dissolved iron is present and the fluid is exposed to natural gamma radiation from the surrounding rock, the growing quartz traps Fe³⁺ in its lattice and develops color centers that read as purple, producing amethyst. When iron concentrations drop or radiation exposure is interrupted, pure or nearly pure quartz grows instead, which appears white or milky due to microscopic fluid inclusions.

The characteristic V-shaped chevron pattern is a direct record of these alternating fluid pulses. Quartz grows fastest along its c-axis, so each pulse of mineralization advances the crystal face forward while the outer edges of neighboring crystals meet in a seam. Viewed in cross section, the layers stack like nested arrowheads pointing toward the termination. The sharper and more uniform the banding, the more rhythmic the original fluid cycling, which usually indicates a relatively stable pocket with repeated recharge events rather than a single rapid fill.

Unlike pure amethyst, which typically grows as isolated terminations lining a geode, chevron material forms where the cavity filled more completely, producing massive banded aggregates rather than pointed crystals. This is why chevron is almost always sold as tumbled pieces, polished spheres, or slabs rather than as single crystals. The milky quartz layers are also why chevron reliably fluoresces only weakly under UV compared to clearer amethyst, since the inclusion-rich bands scatter much of the incoming light.

Chevron amethyst is identified first by the alternating purple and white banding, which follows the growth zones of the original crystal and is visible on any cut or broken surface. Under a loupe, the boundary between layers is sharp but irregular, often showing tiny zigzag steps where crystal faces met. Hardness runs a full 7 on Mohs across both color zones, which distinguishes it from banded fluorite or banded calcite imitators that are much softer. Specific gravity sits at 2.63 to 2.65, consistent with any quartz variety.

The stone is uniaxial positive with a refractive index of 1.544 to 1.553, and the purple zones show weak pleochroism from reddish-violet to bluish-violet when rotated. White bands are never perfectly opaque under strong light, and they transmit a soft internal glow that dyed imitators cannot replicate. Natural chevron never shows dye concentration along fractures, and the white quartz bands should feel continuous with the purple bands rather than looking painted on the surface. A streak test on unglazed porcelain produces white with no color transfer.