Dumortierite

Dumortierite is a mineral containing aluminium, boron and silicon. It usually occurs as fibrous masses of fine, needle-like crystals and is known for its vivid blue colour; greenish blue, violet and brown examples also occur. Massive blue material is used for cabochons and beads. Quartz that contains blue dumortierite needles is called “dumortierite quartz”.

Jewellery and decoration: Massive blue material is worked into cabochons, beads and small carvings. “Dumortierite quartz” is also cut as a faceted stone, showing the blue needles inside crystal quartz. Industry: It is used in making high-grade porcelain. The Champion mine near Oreana in Nevada, USA, was once mined commercially. Collecting: Sprays of needle-like blue crystals and finely crystallised pieces are sought after in mineral collecting.

It has a hardness of 7–8.5 on the Mohs scale. It scratches glass and steel; a steel knife cannot scratch it. Its specific gravity is 3.21–3.41 g/cm³.

Its best-known localities: Chaponost, Rhône, France; Champion mine (near Oreana), Nevada, USA; Quartzsite, La Paz County, Arizona, USA; Dehesa, San Diego County, California, USA; Gföhl unit, Lower Austria.

Its colour is vivid blue, greenish blue, violet, purple or brown. It usually occurs as masses made of fine, needle-like or fibrous crystals. Its hardness is 7–8.5, close to or above quartz. It is much harder than the sodalite (5.5–6) and lapis lazuli (about 5–5.5) it resembles. It shows strong pleochroism: viewed from different directions, the crystals change between deep blue and colourless or very pale blue. Dumortierite can be confused with sodalite or lapis lazuli and has been used as imitation lapis; its hardness and refractive index are different from theirs.

On the “street to diamond” value ladder it sits on step 5 of nine: Ornamental stone. What matters most in dumortierite is the vividness and evenness of the blue, the pattern on the polished surface, and the availability of crack-free, even pieces. Pale or patchy material mixed with rock or quartz is less sought after. Transparent crystals that can be faceted are very rare; most material is opaque or translucent massive rock. Blue needles inside rock crystal quartz (dumortierite quartz) are of interest to collectors.

Today crystal-therapy practitioners claim that dumortierite increases patience, balance and focus, makes it easier to understand others and to progress towards goals, is linked with the throat chakra, and joins the spirit with the body. The same circles claim that dumortierite relieves migraine, sore throats, toothache, sprains and period pain, and helps the thyroid gland, fevers and thymus problems. There is no scientific evidence that dumortierite increases patience and focus or relieves pain, fever or thyroid or thymus problems; for lasting pain, fever or hormonal problems, see a doctor rather than relying on a stone. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.