Dumortierite is named after V.E. Dumortier, a French paleontologist in the 19th century. Its Chinese name is ”蓝线石,” describing its appearance as blue. In the gemstone industry, purple and blue Dumortierite blocks are used as carving and decoration materials, and the curved gem can show the cat’s eye effect.
Dumortierite occurs in aluminous metamorphic rocks and pegmatite rocks, and columnar crystals larger than 1mm are very rare. This kind of material is produced in Nevada, the United States, Brazil, Sri Lanka, France, Madagascar, and Canada.
- Chemical composition: Al,Fe3+)7 (BO3) [SiO4] 3O3.
- Crystal system and crystallization habit: orthorhombic crystal system. Columnar crystals, also in the form of fibrous or massive aggregates, are often coexisted with quartz.
- Hardness: 7-8.
- Relative density: 3.26~3.41.
- Refractive index: 1.686 ～ 1.723.
- Birefringence: 0.037.
- Optical property: negative optical property of the biaxial crystal.
- Transparency: translucent to opaque.
- Gloss: glass luster.
- Color: dark blue, purple-blue, and reddish brown.
- Multicolor: medium, black, dark reddish brown.
- Basic properties of Dumortierite
- Composition: The chemical formula is (A1, Fe3+) 7 [SiO4] 3O3, containing a small amount of Ti, Mg, and P.
Dumortierite Form
Dumortierite belongs to the orthorhombic system, often in columnar and acicular shapes. Sometimes parallel (010) polycrystalline twins can be seen, and fibrous aggregates or blocks can be seen.
The cleavage of {100} is complete, while the cleavage of {110}, {210} is incomplete.
Optical properties of Dumortierite
It is Blue, blue-green, purple, and rose red. Pleochroism is in the slice: Np=dark blue, purple, green, Nm=light blue, light purple, Nm=yellow, Ng=light blue, colorless. The absorbability is Np>Nm>Ng. Positive protrusion. Np=1.659~1.686，Nm=1.684~1.672，Ng=1.686~1.723，Ng-Np=0.027~0.037.
The highest interference color can reach Grade II orange to Grade III blue. Parallel extinction. Negative ductility. The triplets along (110) are visible. Two axis (I), 2V=20 °~40 °. Strong dispersion, r 《μ.
Physical characteristics of Dumortierite
Dumortierite is green-blue, light blue, purple, brown, or pink, with glass luster, transparent to translucent. The biaxial crystal has negative optical properties, V=13~40, the refractive index is N=1.686~1.723, Nm=1.672~1.684, Np=1.659~1.686, and birefringence is 0.027~0.037.
It is strongly trichromatic, Ng is colorless to yellowish green, Nm is yellowish red or nearly colorless, N is dark blue, and the dispersion is 0.023.
It is erotic under ultraviolet fluorescence, and some have blue fluorescence under long-wave ultraviolet light. Dumortierite from California, the United States, is white to purple fluorescence under short-wave ultraviolet light, and Dumortierite from France is blue fluorescence under short-wave. No characteristic absorption spectrum.
The cleavage of parallel (100} is medium, parallel {110} is incomplete, parallel {210} is highly incomplete, the fracture is uneven, the Mohs hardness is 7, and the density is 3.35g/cm.
Where is Dumortierite from
Dumortierite occurs in granite pegmatite vein and atmolith vein and coexists with minerals containing AI, B, Zr, Ce, and Y; and coexists with quartz, muscovite, sillimanite, kyanite, lazulite, etc.
The countries in the world that produce gem-grade Dumortierite include the United States, Brazil, Chile, Liberia, Sri Lanka, Namibia, Madagascar, France, etc.
For example, Nevada in the United States produces purple Dumortierite, and Sri Lanka produces brown transparent Dumortierite crystals.
China has found Dumortierite in Tibet and other places, but its gem value remains to be studied.
Dumortierite Quartz
Dumortierite Quartz crystal is full of iron-rich Dumortierite inclusion particles.
The aluminum contained in the crystal body of Dumortierite can be replaced by iron and titanium, belonging to the orthorhombic system.
The single crystal is columnar, and the aggregate is columnar, massive, and fibrous.
The colors are blue, cyan, green, blue, violet, etc. It has glass luster and good transparency. The hardness is 8 ～ 8.5, the density is 3.26 ～ 3.41g/cm, and it can emit blue, blue-white to purple fluorescence under ultraviolet short wave irradiation.
In terms of arts and crafts, the crystal is required to be bright, pure, and transparent, and the block is dense, tough, and crack-free. When carving, its blue and purple shadows can be used to produce a curved gem with cat’s eye effect.
dumortieritecat’s eye
The gem with cat’s eye effect is made by grinding the fibrous aggregate of Dumortierite.
The faceted Dumortierite can be used as jewelry, ring face, etc., after being processed into an arc-shaped gem. The blue and pink Dumortierite crystals from Nevada in the United States are better in quality, and the blue and white spot Dumortierite from Mexico are also very beautiful in quality.
Dumortierite healing property
Wearing Dumortierite rings or ornaments is conducive to people’s emotional soothing and calmness, helps the blood circulation of the body, improves the function of the digestive system and respiratory systems, and makes people sleep peacefully.
Therefore, the Dumortierite is considered a kind of crystal that is conducive to health and symbolizes that it can bring people a better future.
How to identify Dumortierite
It is somewhat similar to tourmaline; the difference is:
Tourmaline is a uniaxial crystal with stronger absorption, while Dumortierite is a biaxial crystal with relatively weak absorption.
The colorless Dumortierite is somewhat similar to the sillimanite; the difference is: Their ductile and optical symbols are just opposite.
The difference between Dumortierite and lazulite is that the absorption is just the opposite.
Because of its bright color, Dumortierite is mostly used to make girdle-round gemstones, but it is rare.
Dumortierite is somewhat similar to lapis lazuli and sodalite, but lapis lazuli has pyrite inclusions, and sodalite has white vein inclusions, which are low in hardness and easy to distinguish.
Dumortierite is often used to imitate lapis lazuli, and the curved gemstone is lovely.
Conclusion:
Dumortierite is also an island-shaped silicate, which mainly exists in metamorphic rocks or pegmatites containing large amounts of aluminum.
The crystal of Dumortierite is columnar, but it is very rare. The most common is the aggregate of karst, fiber and radiation;
The color is blue, violet, pink, brown, uneven fracture, and the color of streak is white;
It has a glassy or dull luster, from transparent to translucent.
In industry, Dumortierite can be used to make the inner layer of the furnace and gemstone. In the world, Dumortierite is mainly produced in Canada, France, Italy, Madagascar, Namibia, Norway, Poland, Sri Lanka, Arizona, California, Colorado, etc.