Got a photo? Identify rocks instantly with the Rockby app
Open the appDescription
Sodalite is a member of the sodalite group of tectosilicates. It is best known for its rich blue color, often mottled with white calcite or other minerals. It typically occurs as disseminated grains, massive aggregates, or less commonly as well-formed dodecahedral crystals. Sodalite is relatively soft and has a vitreous to greasy luster. It is distinguished from similar blue minerals like lazurite (a component of lapis lazuli) by its lack of pyrite inclusions and its generally lower specific gravity. Some sodalite exhibits tenebrescence, a property where its color changes upon exposure to ultraviolet light and then fades in visible light, a variety known as 'hackmanite'.
How to Identify
- Color
- Typically deep royal blue, but can also be gray, green, yellow, pink, or white. Often mottled with white streaks or patches of calcite.
- Luster
- Vitreous to greasy.
- Texture
- Massive, granular, or as disseminated grains within host rock. Crystals are rare but can be dodecahedral.
- Crystal Form
- Cubic system, typically forming dodecahedra, but more commonly found as massive aggregates or disseminated grains.
- Cleavage
- Poor to distinct in three directions (dodecahedral), but often difficult to observe in massive material.
- Geological Environment
- Found in silica-undersaturated igneous rocks (e.g., nepheline syenites, phonolites) and associated metasomatic rocks (e.g., fenites). It is an indicator mineral for alkaline igneous activity.
Key Facts
- Hardness: 5.5-6 (Mohs scale)
- Specific Gravity: 2.13-2.29 g/cm³
- Crystal System: Cubic
- Color: Deep royal blue (most common), also gray, green, yellow, pink, white
- Luster: Vitreous to greasy
- Transparency: Transparent to opaque
- Fracture: Conchoidal to uneven
- Cleavage: Poor to distinct dodecahedral {110}
- Composition: Sodium aluminum silicate with chlorine
Quick Check
- Color: Deep royal blue (most common), also gray, green, yellow, pink, white
- Luster: Vitreous to greasy
- Streak: White
Physical Characteristics
- Crystal Habit: Massive, granular, disseminated grains; rarely as dodecahedral crystals
- Cleavage Type: Poor to distinct dodecahedral {110}
- Fracture Type: Conchoidal to uneven
- Tenacity: Brittle
- Luster Type: Vitreous to greasy
Formation
Sodalite is a tectosilicate mineral that forms in silica-undersaturated igneous rocks, such as nepheline syenites, phonolites, and other alkaline intrusive and extrusive rocks. It can also form in metasomatic environments, where existing rocks are altered by hot, chemically active fluids, particularly in contact with carbonate rocks or during fenitization processes. The presence of chlorine is crucial for its formation, often derived from magmatic fluids or assimilated country rocks. It crystallizes from late-stage magmatic melts or hydrothermal solutions.
Usage
Sodalite is primarily used as an ornamental stone, for carvings, cabochons, beads, and inlays due to its attractive blue color. It is also used in architectural applications for countertops, tiles, and decorative panels. Historically, it has been used as a pigment (ultramarine blue, though this is more commonly associated with lapis lazuli, which contains sodalite). In scientific research, sodalite and synthetic sodalite-group minerals are studied for their ion-exchange properties, gas storage capabilities, and as host materials for various functional applications.
Age Distribution
Sodalite forms in various geological settings, primarily associated with alkaline igneous rocks, which can range in age from Precambrian to Cenozoic. Its formation is tied to specific magmatic and metasomatic processes rather than a particular geological epoch.
Where to Find
Bancroft, Ontario, Canada
Known for significant deposits of blue sodalite, often associated with nepheline syenite intrusions.
Kola Peninsula, Russia
Home to large alkaline massifs (e.g., Khibiny and Lovozero) where sodalite is a common rock-forming mineral.
Bahia, Brazil
Produces high-quality blue sodalite, often used for ornamental purposes.
Namibia
Significant deposits, particularly in the Kunene region, yielding attractive blue sodalite.
Maine, USA
Occurrences in alkaline pegmatites and syenites.
Greenland
Found in the Ilimaussaq alkaline complex, known for its unique mineralogy including sodalite.
Finding Tips
Look for Alkaline Igneous Rocks
Sodalite is almost exclusively found in silica-undersaturated igneous rocks like nepheline syenites and phonolites. Familiarize yourself with the appearance of these host rocks.
Check for Associated Minerals
Sodalite often occurs with other alkaline minerals such as nepheline, cancrinite, aegirine, and alkali feldspars. The presence of these minerals can indicate a favorable environment.
Observe Color and Luster
The characteristic deep blue color and vitreous to greasy luster are key identifiers. Look for white streaks or patches, which are often calcite inclusions.
Test for Tenebrescence (Hackmanite)
If you have a UV light, test for tenebrescence. Some sodalite (hackmanite) will change color (e.g., from white to pink/purple) under shortwave UV light and then fade in visible light. This is a definitive, though not universal, characteristic.
Consider Hardness
Sodalite is relatively soft (5.5-6 on Mohs scale). It can be scratched by a steel file but will scratch glass. This helps differentiate it from harder blue minerals.
Safety Precautions
Sodalite itself is not considered hazardous. However, always wear appropriate personal protective equipment (PPE) such as gloves and eye protection when collecting rocks, especially in areas with sharp edges or potential for falling debris. Be aware of your surroundings in geological field environments.
Similar Rocks
Lapis Lazuli
Lapis Lazuli (a rock composed primarily of lazurite, calcite, pyrite, and sodalite)
Also known as: Lapis
Lazurite
Lazurite (Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)]
Also known as: None
Dumortierite
Dumortierite (Al7(BO3)(SiO4)3O3)
Also known as: None
Azurite
Azurite (Cu3(CO3)2(OH)2)
Also known as: Chessylite
Scientific Classification
- Mineral Class
- Tectosilicate
- Group
- Sodalite Group
- Crystal System
- Cubic
- Chemical Formula
- Na8(Al6Si6O24)Cl2
- Composition
- Sodium aluminum silicate with chlorine
Explore Sodalite
Identify rocks anywhere
Free on iOS, Android, and Web. Photo identification, full database, and your personal collection.