Uvite Identification Guide
Identify uvite, a calcium-rich tourmaline often forming green or brown crystals in marble, and distinguish it from dravite and schorl.
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What Uvite Looks Like
Uvite is a calcium-rich member of the tourmaline group (a calcium-magnesium tourmaline). It commonly occurs as dark green, olive, brown, or black stubby prismatic crystals, and is especially well known for sharp green or brown crystals embedded in white marble. Crystals show the classic tourmaline rounded-triangular cross-section and lengthwise striations, with a vitreous luster and transparency from opaque to gem-transparent in fine green material. Uvite crystals tend to be shorter and stubbier than the long needles of other tourmalines.
Step-by-Step Field-ID Checklist
- Confirm tourmaline form. Prismatic crystal with a rounded triangular cross-section and striations parallel to the length - diagnostic of the group.
- Note the habit. Stubby, short prisms (uvite trend) rather than long slender needles.
- Check the matrix. Green/brown crystals set in white marble strongly suggest uvite.
- Assess color. Green, olive, brown, or black.
- Hardness test. Scratches glass easily; not scratched by steel.
- Look for no cleavage and conchoidal fracture.
Key Diagnostic Tests
- Mohs hardness: ~7-7.5 (tourmaline group).
- Streak: White.
- Cleavage/fracture: Very poor/no cleavage; conchoidal to uneven fracture.
- Magnetism: None.
- Acid: No reaction (a marble matrix will fizz, helping confirm the carbonate host).
- Density: ~3.0-3.1 g/cm3.
- Pyro/piezoelectricity: Tourmalines develop static charge when heated - a group-level confirmation.
Common Look-Alikes
- Dravite: Sodium-magnesium tourmaline, brown, chemically very close - the two are often hard to separate without analysis, but uvite trends stubbier and is classically marble-hosted; dravite trends brown in metasediments. Lab chemistry (Ca vs Na dominance) is the true separator.
- Schorl: Black sodium-iron tourmaline, typically longer prisms in granite/pegmatite, not marble.
- Green tourmaline (elbaite/verdelite): Lithium-rich, often gemmier and in pegmatites, lower density tendency.
- Epidote/diopside: Have distinct cleavage, unlike tourmaline.
- Green garnet: Isometric dodecahedra, no prismatic striations.
The striated triangular-section prism with no cleavage and a marble host pointing toward calcium-rich chemistry indicates uvite.
Where It Is Found
Uvite forms in metamorphosed limestones and dolomitic marbles and in metasomatic settings. Well-known localities include Brumado (Bahia, Brazil), the Indo-Burmese marbles, Sri Lanka, the USA (e.g., New York), and various marble-hosted occurrences worldwide.
Frequently asked questions
What is uvite?
Uvite is a calcium-rich member of the tourmaline group, commonly forming green, brown, or black stubby crystals, often embedded in white marble.
How do you tell uvite from dravite?
They are chemically very similar (uvite is calcium-dominant, dravite sodium-dominant), so definitive separation needs lab analysis; in the field, uvite tends to be stubbier and classically marble-hosted.
How can you tell if a crystal is uvite tourmaline?
Look for a prismatic crystal with a rounded triangular cross-section, lengthwise striations, no cleavage, hardness around 7-7.5, and often green or brown crystals in white marble.
What color is uvite?
Uvite is usually dark green, olive, brown, or black, with the finest material being transparent green.