Smoky Quartz Identification Guide

What Smoky Quartz Looks Like

Smoky quartz is the brown-to-black, smoky-gray transparent variety of crystalline quartz (SiO₂). Its color, caused by natural irradiation acting on trace aluminum, ranges from pale tan and smoky gray to deep brown and nearly black (very dark material is called morion). It is transparent to translucent with a bright vitreous luster. Crystals show the classic quartz habit: six-sided (hexagonal) prisms striated horizontally across the faces, terminated by six-sided pyramidal points. Color is often zoned, darker toward the tips.

Step-by-Step Field ID Checklist

1. Check the color and clarity. Look for see-through smoky brown to gray, not opaque. Even dark stones transmit light at thin edges.
2. Look at crystal form. Hexagonal prisms with horizontal striations and pyramidal terminations strongly indicate quartz.
3. Test hardness. It scratches glass and steel easily (Mohs 7) and is not scratched by a knife.
4. Examine fracture. Broken (non-crystal) surfaces show smooth, curved conchoidal fracture; quartz has no cleavage.
5. Feel it. Quartz feels cool and is moderately light.
6. Watch for color even-ness. Natural smoky color is often zoned; uniformly very dark stones may be irradiated or heat-altered amethyst/clear quartz.

Key Diagnostic Tests

• Hardness: 7 — scratches glass and steel; this rules out most softer brown stones.
• Streak: White (the mineral is too hard to streak on a normal plate; powder is colorless).
• Cleavage/fracture: No cleavage; conchoidal fracture.
• Density: About 2.65 g/cm³.
• Acid: No reaction.
• Optics: Uniaxial, with no pleochroism strong enough to mistake for tourmaline; no double-image as strong as calcite.

Common Look-Alikes and How to Tell Them Apart

• Smoky obsidian/glass: Softer (~5.5) volcanic glass with no crystal faces; quartz is harder and often shows hexagonal prisms.
• Smoky topaz (often misnamed): True topaz is harder (8), has perfect basal cleavage, and higher density; much "smoky topaz" sold commercially is actually smoky quartz or treated material.
• Brown tourmaline (dravite): Often shows a rounded-triangular cross-section, strong pleochroism, and vertical (not horizontal) striations.
• Citrine/heat-treated stones: A warm honey-brown rather than true smoky gray; smoky quartz holds a cooler grayish tone.
• Andalusite/axinite: Strong pleochroism and different crystal forms distinguish these.

Where Smoky Quartz Is Found

Smoky quartz is common worldwide, especially in granites and granitic pegmatites where natural radiation darkens the quartz. Notable localities include the Swiss and French Alps, Scotland (Cairngorm Mountains, the source of "cairngorm" stone), Brazil, Madagascar, the Pikes Peak granite of Colorado, the Alps, and many pegmatite districts. Look in weathered granite, miarolitic cavities, pegmatite pockets, and stream gravels downslope from such rocks.