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Cavansite on Stilbite refers to a mineral specimen where vibrant blue cavansite crystals are found growing on a matrix of stilbite. Cavansite is a rare calcium vanadium oxysilicate mineral, known for its intense blue to greenish-blue color and characteristic spherical or radiating crystal aggregates. Stilbite-Ca is a common zeolite mineral, typically white, cream, or salmon-pink, forming tabular or sheaf-like crystals. The contrast between the deep blue cavansite and the lighter-colored stilbite creates highly aesthetic and sought-after mineral specimens.
How to Identify
- Color
- Cavansite: Intense blue to greenish-blue. Stilbite: White, cream, salmon-pink, or brownish-yellow.
- Luster
- Cavansite: Vitreous to pearly. Stilbite: Vitreous to pearly.
- Texture
- Cavansite: Typically forms radiating aggregates, often spherical or 'puffball' like. Stilbite: Tabular, sheaf-like, or radiating aggregates.
- Crystal Form
- Cavansite: Orthorhombic, often forming radiating acicular crystals in spherical aggregates up to several centimeters in diameter. Stilbite: Monoclinic, typically forming tabular crystals, often in characteristic 'sheaf' or 'bow-tie' aggregates.
- Cleavage
- Cavansite: Perfect on {010}. Stilbite: Perfect on {010}.
- Geological Environment
- Amygdaloidal cavities and fractures within basaltic and other mafic volcanic rocks, often associated with other zeolites, apophyllite, and calcite.
Key Facts
- Hardness: Cavansite: 3-4 (Mohs); Stilbite: 3.5-4 (Mohs)
- Specific Gravity: Cavansite: 2.21-2.33; Stilbite: 2.1-2.2
- Crystal System: Cavansite: Orthorhombic; Stilbite: Monoclinic
- Color: Cavansite: Intense blue to greenish-blue; Stilbite: White, cream, salmon-pink, brownish-yellow
- Luster: Vitreous to pearly
- Transparency: Transparent to translucent
- Fracture: Cavansite: Uneven; Stilbite: Uneven to subconchoidal
- Cleavage: Cavansite: Perfect on {010}; Stilbite: Perfect on {010}
- Composition: Cavansite: Hydrated calcium vanadium oxysilicate; Stilbite: Hydrated sodium calcium aluminum silicate
Quick Check
- Color: Cavansite: Deep blue; Stilbite: White to salmon-pink.
- Luster: Vitreous to pearly.
- Streak: Cavansite: Pale blue; Stilbite: White.
Physical Characteristics
- Crystal Habit: Cavansite: Radiating aggregates, spherical 'puffballs', acicular crystals. Stilbite: Tabular, sheaf-like, radiating aggregates, often forming 'bow-ties'.
- Cleavage Type: Cavansite: Perfect basal cleavage; Stilbite: Perfect basal cleavage.
- Fracture Type: Cavansite: Uneven; Stilbite: Uneven to subconchoidal.
- Tenacity: Cavansite: Brittle; Stilbite: Brittle.
- Luster Type: Vitreous to pearly.
Formation
Cavansite and Stilbite typically form in the amygdaloidal cavities and fractures of basaltic and other mafic volcanic rocks. They are secondary minerals, precipitating from hydrothermal solutions rich in calcium, vanadium, silicon, and aluminum, often at low temperatures and pressures. The presence of both minerals together indicates a specific geochemical environment where these elements were available and conditions were suitable for their sequential or co-precipitation. Stilbite, a zeolite, often forms first, lining the cavities, and then cavansite crystallizes on its surface.
Usage
Primarily a collector's mineral due to its striking color and aesthetic crystal habits. It has no significant industrial or commercial uses.
Age Distribution
Formed in relatively recent geological times, often associated with Cenozoic basaltic volcanism.
Where to Find
Wagholi Quarries, Pune District, Maharashtra, India
The most famous and prolific locality for high-quality cavansite on stilbite specimens. These quarries are known for their extensive basalt flows of the Deccan Traps, which host numerous zeolite-filled amygdales.
Malheur County, Oregon, USA
Known for some occurrences of cavansite, though specimens are generally less abundant and aesthetic than those from India.
New Zealand
Minor occurrences have been reported in basaltic rocks.
Finding Tips
Geological Context
Focus on areas with Cenozoic basaltic volcanic rocks, particularly those with amygdaloidal structures or hydrothermal alteration zones. Cavansite and stilbite are secondary minerals, so look for them in cavities and veins within the host rock.
Associated Minerals
Cavansite and stilbite are often found with other zeolites (e.g., heulandite, scolecite, laumontite), apophyllite, and calcite. The presence of these minerals can indicate a favorable environment for cavansite formation.
Careful Extraction
Both cavansite and stilbite crystals can be delicate. Use appropriate tools for careful extraction to preserve the aesthetic quality of the specimen. Cavansite's radiating aggregates are particularly fragile.
Visual Identification
Look for the distinctive intense blue color of cavansite 'puffballs' or radiating sprays against the lighter background of stilbite crystals. Stilbite's characteristic sheaf-like or tabular crystals are also a good indicator.
Similar Rocks
Pentagonite on Stilbite
Pentagonite (Ca(VO)Si4O10·4H2O) on Stilbite-Ca ((Na,Ca)2-3Al3(Al,Si)2Si13O36·14H2O)
Also known as: Pentagonite with Stilbite
Apophyllite with Stilbite
Apophyllite group minerals (e.g., KCa4(Si8O20)(F,OH)·8H2O) with Stilbite-Ca ((Na,Ca)2-3Al3(Al,Si)2Si13O36·14H2O)
Also known as: Apophyllite on Stilbite
Heulandite with Stilbite
Heulandite group minerals ((Ca,Na)2-3Al3(Al,Si)2Si13O36·14H2O) with Stilbite-Ca ((Na,Ca)2-3Al3(Al,Si)2Si13O36·14H2O)
Also known as: Heulandite on Stilbite
Scientific Classification
- Mineral Class
- Cavansite: Phyllosilicate; Stilbite: Tectosilicate (Zeolite Group)
- Group
- Cavansite: Cavansite Group; Stilbite: Zeolite Group (Heulandite-Stilbite Series)
- Crystal System
- Cavansite: Orthorhombic; Stilbite: Monoclinic
- Chemical Formula
- Cavansite: Ca(VO)Si4O10·4H2O; Stilbite-Ca: (Na,Ca)2-3Al3(Al,Si)2Si13O36·14H2O
- Composition
- Cavansite: Calcium, Vanadium, Silicon, Oxygen, Hydrogen; Stilbite: Sodium, Calcium, Aluminum, Silicon, Oxygen, Hydrogen
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