Dumortierite Quartz: Rare Blue Quartz

Dumortierite quartz is blue colored quartz containing abundant dumortierite inclusions.

Dumortierite quartz is one of the rarer and more unusual blue varieties of quartz gemstones. It is a gemstone-quality combination of quartz aggregate, intergrown with the mineral known as dumortierite. Although quartz can occur in a wide range of colors, blue colored quartz is surprisingly quite rare. The traces of dumortierite are responsible for its distinct color, which can range from light to dark blue and in some cases reddish-brown.

How Dumortierite Quartz is Formed

Dumortierite Quartz is typically found in hydrothermal veins, which are formed when hot, mineral-rich fluids flow through rocks.

The formation of Dumortierite Quartz begins with the weathering and erosion of rocks that contain dumortierite. This dumortierite is then transported by water or other fluids to a hydrothermal vein.

In the hydrothermal vein, the dumortierite is dissolved by the hot, mineral-rich fluids. The fluids then cool and the dumortierite crystallizes out of solution. This crystallization process can form Dumortierite Quartz in a variety of shapes and sizes.

Dumortierite Quartz is typically found in association with other hydrothermal minerals, such as quartz, calcite, and fluorite. It is often found in veins that are associated with igneous rocks, such as granite and rhyolite.

Dumortierite-quartz specimen - Brazil Photo: James St. John

Dumortierite

Dumortierite is a rare and beautiful mineral that is prized for its vibrant blue color. It is a borosilicate of aluminum, with the chemical formula  Al₇BO₃(SiO₄)₃O₃. Dumortierite typically occurs in fibrous aggregates of slender prismatic crystals, and it can range in color from pale blue to deep violet-blue.

Dumortierite is typically found in fibrous or needle-like crystals that can be up to several centimeters in length. It is also found in massive or granular forms. The color of dumortierite can vary from pale blue to deep blue-green, depending on the iron content.

Dumortierite is found in a variety of geological settings, including high-grade metamorphic rocks, contact metamorphic rocks, and pegmatites. It is also found in some alluvial deposits. The primary sources of dumortierite are Brazil, Madagascar, Sri Lanka, and the United States.

Dumortierite is a relatively hard mineral, with a Mohs hardness of 7 to 8. It is also translucent to opaque. Dumortierite is sometimes mistaken for other blue minerals, such as sodalite and lapis lazuli. However, it can be distinguished from these minerals by its higher hardness and fibrous habit.

The mineral was first described in 1881 and was named after French paleontologist, Eugene Dumortier (1803-1873). Dumortierite also has a few industrial purposes other than jewelry. Since it is known to turn remarkably pure white in color when fired, it is often used for the production of porcelain and ceramics. It is sometimes mistaken for sodalite and has been used as imitation lapis lazuli. 

Quartz with Dumortierite Inclusions Photo © Jeff Scovil

Dumortierite Quartz properties

Composition: Dumortierite quartz is primarily composed of silicon dioxide (SiO2), which is the chemical composition of quartz, along with inclusions of dumortierite (Al₃(BO₃)(SiO₃)₂), which is an aluminum borosilicate mineral.

Color: Dumortierite quartz typically exhibits a blue to violet-blue color due to the presence of dumortierite inclusions, although it can also occur in other colors such as pink, brown, or gray.

Luster: Vitreous to dull.

Crystal System: Quartz: trigonal; Dumortierite: orthorhombic

Streak: Usually colorless or white.

Hardness: 7 on the Mohs scale, the same as quartz.

Cleavage: Dumortierite quartz typically does not exhibit cleavage as it fractures conchoidally.

Crystal Form: Typically occurs as prismatic hexagonal crystals, but often forms massive aggregates with fibrous texture due to the inclusion of dumortierite.

Density: The density of dumortierite quartz ranges from approximately 2.65 to 3.35 g/cm^3.

Transparency: Generally translucent to opaque due to the included dumortierite fibers.

Fracture: Conchoidal fracture, which means it breaks with smooth, curved surfaces.

Specific Gravity: Typically ranges from 2.65 to 3.35, depending on the amount of dumortierite inclusion.

Solubility: Insoluble in water and acids.

Magnetism: Generally not magnetic unless there are magnetic impurities present.

Fluorescence: Dumortierite quartz may exhibit fluorescence under ultraviolet light, but it's not a universal trait and can vary depending on the specimen.

Pleochroism: Dumortierite quartz may exhibit weak to moderate pleochroism, showing different colors when viewed from different angles due to the orientation of the dumortierite fibers.

Refractive Index: The refractive index of dumortierite quartz is typically around 1.544 to 1.553 for the ordinary ray (alpha), and 1.553 to 1.554 for the extraordinary ray (beta), with a birefringence of about 0.009 to 0.011.

Inclusions: The defining feature of Dumortierite Quartz is the presence of visible inclusions of the mineral dumortierite. These inclusions can vary in size, shape, and color, but they are typically fibrous, needle-like, or feathery and range in color from blue, violet, green, to brown.

Dumortierite Quartz Uses

Dumortierite quartz is a unique and visually appealing gemstone that has some interesting properties, but it is not as widely used as some other gemstones. Here are some common uses and applications of dumortierite quartz:

Gemstone and Jewelry:

Dumortierite quartz is cut and polished into cabochons, beads, and faceted stones for use in jewelry.

Its distinctive blue to violet-blue color, combined with the fibrous inclusions, makes it a unique and attractive gemstone for use in rings, pendants, earrings, and other jewelry pieces.

Ornamental Stone:

The aesthetic appeal of dumortierite quartz, with its rich blue color and fibrous texture, makes it a popular choice for ornamental carvings, sculptures, and decorative objects.

Collectibles and Specimens:

Dumortierite quartz specimens are collected by mineral enthusiasts and collectors due to their rarity and unique appearance.

Some collectors value dumortierite quartz for its interesting inclusions and the way it showcases the interplay between quartz and dumortierite.

Metaphysical and Healing Properties:

Like many gemstones, dumortierite quartz is believed by some to have metaphysical properties and healing energies.

It is often associated with qualities such as clarity of thought, communication, and personal expression.

Some people use dumortierite quartz in meditation and energy work.

Art and Craft:

The unique appearance of dumortierite quartz makes it a valuable material for artists and crafters.

It may be incorporated into sculptures, mosaics, or mixed media art projects for its aesthetic appeal.

Lapidary Work:

Lapidarists and artisans may use dumortierite quartz for lapidary work, creating custom pieces and unique designs.

Dumortierite Quartz -Brazil Photo: László Kupi