Geological Properties Of Dravite

Introduction

Dravite is a sodium magnesium-rich variety of tourmaline, distinguished by its deep brown to golden-brown color. It belongs to the complex borosilicate mineral group known for its wide color range and intricate chemistry. The name Dravite originates from the Drava River region in Carinthia, Austria, where the mineral was first identified in the 1880s.

Unlike its better-known siblings such as Elbaite (green, pink, blue tourmaline) or Schorl (black tourmaline), Dravite’s earthy tones come from magnesium and iron content rather than lithium or manganese. It forms in metamorphic rocks rich in magnesium, such as schists, marbles, and dolomitic limestones, as well as in pegmatites.

Geological Properties Of Dravite, Dravite is a member that is rare of Tourmaline Group of minerals that includes Achroite, Dravite, Liddicoatite, Povondraite, Rubellite, Uvite and Schorl. Dravite is a magnesium member that is rich of Tourmaline Group. Other more common and more well know Tourmalines are Elbaite colors that are(various colorless, lithium rich), Schorl (opaque black, iron rich), Uvite and Liddicoatite. Most Tourmaline that is colored used gemstones are Elbaite Tourmaline. Dravite is named for the river Drau (in Latin, Drave), on that the kind locality is found. Its available in colors of brown to black, red, yellow, blue, green, colorless, colorless and white to yellow in thin section.

Distribution: Discovered around Dravograd (Unterdrauberg), Slovenia. From Beura, Val d’Ossola, Piedmont, Italy. At Arendal and Snarum, Norway. From Outokumpu, and Kaavi, Kuopio, Finland. In the USA, ¯ne crystals from Gouverneur, Pierrepont, and Macomb, St. Lawrence Co., New York; at Franklin and Hamburg, Sussex Co., New Jersey; and Newry, Oxford Co., Maine. In Canada, in Hull Township, Quebec; at Wilberforce, Ontario; and a number of other places. From Brumado, Bahia, Brazil. Large crystals from Yinnietharra, 800 km north of Perth, Western Australia. At Osarara, Narok district, Kenya. From Gujarkot, Nepal. Increasingly distinguished from other tourmaline group members.

In a few rare instances, Dravite may be partially replaced or intergrown together with Schorl, with a specimen being part Dravite and part Schorl. Dravite is also very similar to Uvite Tourmaline, and often occurs together with Uvite in Uvite deposits. It can sometimes be very difficult to make an exact distinction between the Dravite and the Uvite.

Dravite, also known as Brown Tourmaline, is a sodium magnesium member of the Tourmaline family. It is a relatively common form of Tourmaline and is known for its attractive brown to black colors and interesting crystal structures. Here are some key geological properties and characteristics of Dravite:

• Chemical Composition: Dravite has the chemical formula Na(Mg3)Al6(Si6O18)(BO3)3(OH)3(OH). It is the magnesium analogue of schorl and the OH analogue of fluor-dravite. It is also known for its green-to-red color change in Cr-bearing varieties, caused by the Usambara effect, which is similar to the alexandrite effect.
• Occurrence and Distribution: Dravite is found in various locations around the globe. It is named after Dravograd, in Slovenia, the area where it was first described. It is also found in pegmatites, with some specimens having the highest amount of rare earth elements (REE) for a pegmatitic tourmaline, although this is still a trace amount (1200 ppm).
• Physical Properties: Dravite, like other tourmaline minerals, has a range of uses and applications, primarily driven by its unique properties and characteristics. It is used as a gemstone in jewelry due to its brown to black colors. It has a hardness suitable for jewelry and rates 7 to 7.5 on the hardness scale. It is also known for its vitreous luster.
• Crystal Structure: Crystals of Dravite from certain localities can be highly lustrous and beautifully crystallized. In some rare instances, Dravite may be partially replaced or intergrown together with Schorl, and it is also very similar to Uvite Tourmaline, often occurring together with Uvite in Uvite deposits.
• High-Pressure Behavior: The high-pressure behavior of dravite tourmaline has been studied using luminescence spectroscopy and synchrotron-based single-crystal diffraction. Emission bands associated with Cr3+/V2+ substitution are constant in energy up to a certain pressure and shift to longer wavelengths at higher pressures, suggesting a change in compressional mechanism.
  

 

Optical and Geological Significance

Dravite’s pleochroism — showing different colors from different angles — is a defining optical property of the Tourmaline family. Under polarized light, it can display golden, reddish-brown, and deep chocolate hues, depending on its crystal orientation.

From a geological standpoint, Dravite serves as an important indicator mineral for boron and magnesium-rich metamorphic conditions. Its presence helps geologists reconstruct:

• The chemical environment during metamorphism.
• Fluid composition and boron transport in the crust.
• The temperature-pressure conditions of regional metamorphic zones.

It often forms in association with:

• Talc
• Chlorite
• Muscovite
• Calcite
• Dolomite
• Quartz

Geological Classification

• Mineral Type: Complex borosilicate
• Formation Type: Regional metamorphism & pegmatitic crystallization
• Host Rocks: Dolomitic marbles, schists, and metamorphosed limestones
• Associated Minerals: Quartz, calcite, talc, chlorite, biotite, schorl

The History And Origin Of Dravite

The history and origin of Dravite, also known as Brown Tourmaline, are rooted in its discovery and naming, as well as its unique geological characteristics.Discovery and Naming: Dravite was first identified near the Drava River in Dravograd, Slovenia. The name “dravite” is derived from this location, and it was first used in 1884 by Gustav Tschermak, a Professor of mineralogy and petrography at the University of Vienna.

Geological Significance: Dravite is a member of the tourmaline family and is known for its brown to brownish-black color, sometimes ranging to dark yellow to dark orange-brown. It is commonly referred to as brown tourmaline and is typically found in association with pegmatites. It is a relatively common form of tourmaline and is known for its unique geological properties.

Crystal Characteristics: Dravite crystals from certain localities can be highly lustrous and beautifully crystallized. It is a relatively common form of tourmaline, often forming in crude uninteresting formations, but with some specimens exhibiting exceptional luster and crystal structure.

In summary, the history and origin of Dravite are closely tied to its discovery near the Drava River in Slovenia and its subsequent naming by Gustav Tschermak. Its unique geological characteristics and crystal properties contribute to its significance as a member of the tourmaline family.

 

Key Localities

Dravite has been discovered in numerous notable geological regions around the world, including:

• Austria – Type locality (Drava River region)
• Slovenia – Classic metamorphic deposits with gem-quality crystals
• Sri Lanka – Honey-colored transparent crystals in metamorphic rocks
• Brazil – Pegmatitic and metamorphic occurrences
• Finland – Brown tourmaline associated with magnesium schists
• Australia (Western Australia) – Fine dark Dravite found in metamorphosed limestone
• Tanzania and Kenya – Deep brown crystals with iron-rich zoning

Each locality’s chemistry subtly influences Dravite’s hue — from golden-honey to nearly black.

 

Discovering the Mineralogical Characteristics of Dravite

The mineralogical characteristics of Dravite, a member of the tourmaline group, can be summarized as follows:

• Chemical Composition: Dravite has a chemical formula of Na(Mg3)Al6(Si6O18)(BO3)3(OH)3(OH), indicating its composition of sodium, magnesium, aluminum, silicon, boron, and hydroxide ions. It is a magnesium-rich variety of tourmaline.
• Color Variations: Dravite is typically brown in color, but it can also appear in green or black variations. It is known for its dark brown and almost black variety within the tourmaline group.
• Crystal Structure: Dravite, like other tourmaline minerals, is characterized by a complex crystal structure. It belongs to the tourmaline supergroup, which comprises a wide range of chemical compositions and endmember formulae.
• Occurrence and Formation: Dravite is typically found in metamorphic rocks that have undergone high pressure and temperature conditions. It is associated with geological environments such as schists, marbles, granites, and pegmatites.
• Historical Significance: The name “Dravite” is derived from the Drava River in Austria, where the mineral was first discovered in the 19th century. It is also associated with a deposit near the river Drave in Carinthia, Austria.

In summary, Dravite exhibits specific chemical composition, color variations, and a complex crystal structure within the tourmaline group. Its occurrence in metamorphic rocks and association with specific geological environments contribute to its mineralogical characteristics and historical significance.

How Dravite Is Formed

The formation of Dravite, also known as Brown Tourmaline, is a result of specific geological processes and conditions. Dravite is a variety of Tourmaline that is rich in sodium and magnesium, and it is typically formed in pegmatites. Here’s a brief overview of how Dravite is formed:

• Pegmatite Formation: Dravite is often found in pegmatites, which are coarse-grained igneous rocks typically found in association with granitic intrusions. Pegmatites are known for their large crystals and can contain a variety of minerals, including tourmaline.
• Specific Chemical Conditions: The formation of Dravite is influenced by specific chemical conditions, including the presence of sodium, magnesium, aluminum, boron, and silicon. These elements combine under the right conditions to form the characteristic composition of Dravite.
• Geological Context: Dravite is named after the Drava River area in Slovenia, where it was first identified. The geological context of this region, including the presence of specific rock formations and mineral deposits, likely played a role in the formation of Dravite.
• Crystal Growth: Dravite forms well-shaped crystals, and its growth is influenced by the surrounding geological environment. The specific conditions within the pegmatite, including temperature, pressure, and chemical interactions, contribute to the crystal growth of Dravite.

In summary, Dravite is formed through the interplay of specific geological conditions, chemical compositions, and crystal growth processes within pegmatite formations. These factors contribute to the unique properties and characteristics of Dravite as a mineral.

Investigating the Metamorphic History Dravite

Dravite, a member of the tourmaline family, is commonly found in metamorphosed limestones or mafic igneous rocks, and occasionally in pegmatites and sedimentary rocks. It is associated with high-pressure, high-temperature environments, such as granites, granitic pegmatites, high-temperature hydrothermal veins, and metamorphic rocks. The mineral’s occurrence in these geological settings reflects its metamorphic history and the conditions under which it forms. Studies have characterized metamorphic Na- and OH-rich disordered dravite with tetrahedral boron, shedding light on its chemistry, structure, and associated minerals. Additionally, the mineral’s historical significance is tied to its original discovery near the Drava River in Dravograd, Slovenia, and its subsequent identification as a tourmaline species. Dravite’s physical properties, including its hardness, specific gravity, and color variations, contribute to its unique characteristics and its suitability for use in jewelry and ornamental objects.

Examining the Structural Properties of Dravite

The structural properties of Dravite, also known as Brown Tourmaline, are a subject of scientific interest and have been studied extensively.

• Crystal Structure Studies: Research has been conducted to understand the crystal structure of Dravite. Studies have focused on the reassignment of cation site occupancies in tourmaline, specifically the Al-Mg disorder in the crystal structure of dravite. This research sheds light on the specific arrangement of cations within the crystal lattice of Dravite, providing insights into its structural properties .
• Chemical Disorder and Structural Characteristics: The link between structure and chemistry in the schorl-dravite series has been explored, highlighting the interplay between chemical composition and the crystal structure of Dravite. This research contributes to a deeper understanding of the structural characteristics of Dravite and its relationship to other tourmaline varieties .
• Metamorphic Variations: Studies have also investigated metamorphic Na- and OH-rich disordered dravite with tetrahedral boron, providing insights into variations in the chemical and structural properties of Dravite under different geological conditions. This research contributes to understanding the structural variations of Dravite in different geological settings .
• Theoretical Studies: Theoretical studies using density functional theory have been employed to investigate the vibrational stretching properties of OH groups in ideal and chemically disordered dravite models. These studies provide theoretical insights into the structural behavior of Dravite at the molecular level, shedding light on its vibrational properties and chemical disorder .

In summary, the structural properties of Dravite have been the subject of scientific investigation, with studies focusing on its crystal structure, chemical disorder, metamorphic variations, and theoretical vibrational properties. These studies contribute to a deeper understanding of the unique structural characteristics of Dravite within the tourmaline family.

 

Physical Properties Of Dravite

The physical properties of Dravite, a member of the tourmaline family, can be summarized as follows:

1. Hardness and Specific Gravity: Dravite has a hardness of 7-7.5 on the Mohs scale, indicating that it is relatively hard and capable of scratching glass. Additionally, it has a specific gravity of 3.1-3.2, making it heavier than most minerals of similar size.
2. Color Variations: Dravite is typically brown in color, but it can also appear in green or black variations.
3. Crystal Structure: Dravite is known for its complex crystal structure, which is characteristic of the tourmaline group of minerals. Its crystal structure has been the subject of scientific studies, including investigations into cation ordering at octahedral sites and thermal stability of extended clusters.
4. Occurrence and Formation: Dravite is found in metamorphic rocks that have undergone high pressure and temperature conditions. It is associated with granites, granitic pegmatites, and high-temperature hydrothermal veins.

In summary, Dravite exhibits a notable hardness, specific gravity, and color variations, and it is characterized by a complex crystal structure. Its occurrence in metamorphic rocks and association with specific geological environments contribute to its unique physical properties.

 

Durability and Maintenance

Dravite’s relatively high hardness (7–7.5) makes it suitable for both ornamental and jewelry purposes. However, it should still be handled gently due to its brittle nature and tendency to fracture under sharp impact.

• Clean with mild soap and lukewarm water.
• Avoid ultrasonic and steam cleaners.
• Store separately to prevent scratching other softer crystals.

 

At Crystals by Rob

At Crystals by Rob, we appreciate Dravite as one of the most grounding geological marvels of the tourmaline family — a stone born from Earth’s transformative heat and pressure. Each specimen reveals nature’s ability to blend stability with transformation, showcasing how beauty forms even in the most intense geological environments.

Our collection highlights authentic, ethically sourced Dravite crystals that embody both the scientific wonder and spiritual grounding that this mineral represents.