Dumortierite Quartz Identification Guide
Identify dumortierite quartz, the blue quartz colored by dumortierite inclusions, and learn how it differs from solid dumortierite, sodalite, and blue chalcedony.
Read the full Dumortierite Quartz encyclopedia entry →
What It Looks Like
Dumortierite quartz is massive quartz that owes its blue to violet color to abundant tiny fibers of included dumortierite. It is usually translucent to opaque, with a vitreous luster and a soft, denim-blue to lavender-blue color that can be patchy or streaky where the inclusions cluster. Often sold as tumbled stones, cabochons, and beads, it sometimes shows pale grayish-white quartz zones between bluer areas.
Telltale Visual Cues
- Mottled or streaky blue distribution — color follows the included fibers, not even dye.
- Quartz vitreous luster with a slightly cloudy translucency.
- Hardness of quartz (7) throughout, since the bulk is silica.
Step-by-Step Field-ID Checklist
- Look at color distribution: uneven, fibrous blue patches suggest mineral inclusions rather than dye.
- Test hardness: scratches glass and steel (Mohs ~7) — it is quartz-dominant.
- Check translucency: hold to light; expect cloudy translucence with denser blue zones.
- Inspect under magnification: look for fine blue fibrous inclusions in clear quartz.
- Confirm conchoidal fracture and absence of cleavage.
- Compare density: close to ordinary quartz (~2.65), lighter than solid dumortierite.
Key Diagnostic Tests
- Mohs hardness: ~7 (quartz host); scratches glass and steel.
- Streak: white.
- Fracture: conchoidal; no cleavage.
- Density: ~2.65 g/cm³ — lighter than pure dumortierite (~3.3).
- Acid: inert to dilute HCl.
- Magnification: reveals fibrous inclusions, distinguishing it from dyed or solid-color stones.
Common Look-Alikes
- Solid dumortierite: denser (~3.3 vs 2.65) and more uniformly colored, with a fibrous body rather than clear quartz host.
- Sodalite: softer (5.5–6, scratched by steel) and lighter, with white veins.
- Blue chalcedony: more even, waxy, and translucent without fibrous patches.
- Dyed blue quartz/howlite: dye sits in cracks and looks artificially even; howlite is far softer (3.5).
- Lapis lazuli: deep blue with pyrite and softer than quartz.
Where It Is Found
Dumortierite quartz is found wherever dumortierite forms within or alongside quartz in aluminum-rich metamorphic and pegmatitic rocks. Major sources include Brazil (a primary commercial supply), Madagascar, Namibia, and the USA. It is commonly marketed as "blue quartz" alongside other inclusion-colored quartzes.
Frequently asked questions
What is dumortierite quartz?
It is quartz colored blue to violet by countless microscopic fibers of the mineral dumortierite trapped inside it. The bulk is silica, so it behaves like quartz with a denim-blue color.
How do you tell dumortierite quartz from solid dumortierite?
Dumortierite quartz is lighter (density ~2.65 vs ~3.3), more translucent with a glassy quartz host, and shows patchy fibrous blue. Solid dumortierite is denser and more uniformly colored throughout.
Is blue quartz the same as dumortierite quartz?
Often, yes. Much of the blue quartz on the market gets its color from dumortierite inclusions, though some blue quartz is colored by other minerals like tourmaline or by light scattering.
How can you tell dumortierite quartz from dyed quartz?
Use magnification: dumortierite quartz shows fibrous blue inclusions distributed through the stone, while dyed quartz has color concentrated in cracks and an unnaturally even surface tint.
Dumortierite Quartz identified by the community
Recent Dumortierite Quartz specimens identified with Rock Identifier.
