Material
One mineral
Prehnite is a distinct mineral. These 5 records compare aggregate forms and associations.
Stone Explorer → Prehnite comparison tool
Prehnite specimens, side by side.
Compare 5 natural prehnite specimens, then follow one growth pathway through openings in rock.
Prehnite file · 5 natural specimen records
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Each specimen opens its own file.
Evidence
What the image can show.
Use the images to compare stones. Check the record for identity and treatment.
Appearance
Rounds and branches
Compare the aggregate outline, translucent areas and associated minerals.
Records
The individual specimen
Localities follow the catalogue entries. Treatment is unrecorded for these 5 specimens.
Sources
Sources + specimen credits
Mineralogy, locality records and photographic evidence.
One mineral, several formsMaterial and evidence
Prehnite is a hydrous calcium aluminium silicate in the orthorhombic crystal system. Rounded, fanlike and stalactitic describe aggregate forms. Locality labels identify the individual records.
Dark crystals and inclusionsMaterial and evidence
The Djouga photo is catalogued as prehnite with epidote. Studies of Mali material also identify amphibole among elongated inclusions. Each mineral identification belongs to its own specimen.
Hammer, Brandstätter & Ponahlo · 2004 · Épidote_et_préhnite_(Kayes_-_Mali)_1.jpg
Formation and timeMaterial and evidence
Prehnite occurs in hydrothermal and low-grade metamorphic settings. The 800–600 million-year range in the Mali study concerns host sedimentary rocks. Newly grown prehnite was also recorded within a 472-day observation window in a New Zealand geothermal well.
Handbook of Mineralogy · Prehnite · GIA · Summer 2006, Mali prehnite · Browne, Courtney & Wood · 1989
Treatment and careMaterial and evidence
Prehnite has a Mohs hardness of about 6–6.5, with cleavage and brittle behaviour. GIA recorded oiling in some Mali material. Treatment is unrecorded for the 5 photographed specimens.
Handbook of Mineralogy · Prehnite · GIA · Summer 2006, Mali prehnite
Names and historyMaterial and evidence
The name honours Hendrik von Prehn. Werner used it in 1788; later historical research places its final establishment in 1793. “Prehnite jade” is a trade name. Prehnite, jadeite and nephrite have different mineral identities.
Cairncross & Master · 2024 · Hammer, Brandstätter & Ponahlo · 2004
Prehnite with epidoteCC BY-SA 3.0
Parent Géry, via Wikimedia Commons · CC BY-SA 3.0
Proportionally resized and saved as WebP; colours unchanged. Cropped in the overview, full photograph in the file.
Paterson prehniteCC BY-SA 3.0
Rob Lavinsky, iRocks.com, via Wikimedia Commons · CC BY-SA 3.0
Proportionally resized and saved as WebP; colours unchanged. Cropped in the overview, full photograph in the file.
Lonavala prehniteCC BY-SA 3.0
Rob Lavinsky, iRocks.com, via Wikimedia Commons · CC BY-SA 3.0
Proportionally resized and saved as WebP; colours unchanged. Cropped in the overview, full photograph in the file.
Formation drawingOne possible pathway
The cutaway shows one hydrothermal pathway in mafic rock. Cavities and aggregates are enlarged schematically. The model represents no particular deposit.
Crystals and aggregatesMaterial reference
Prehnite occurs as rounded botryoidal or kidney-shaped masses, radiating fans, stalactitic forms and individual tabular or prismatic crystals. The Imilchil and GeoDIL records show plates within fans; the Paterson record shows a stalactitic form. A pseudomorph retains the shape of an earlier mineral and belongs to its specific specimen record.
Open sourceColour and transparencyMaterial reference
Green, yellow-green, yellow and white occur in prehnite; grey and pink are less familiar reported colours. Colour, cloudiness and crystal habit are separate observations. The pale fans and the deeper green rounded Mali material provide different views of these features, without creating separate mineral species.
Open sourceAssociation and inclusionMaterial reference
Epidote is documented with prehnite in the Mali reference. A crystal growing beside prehnite is an external association; a crystal enclosed inside it is an inclusion. Dark needles in another specimen need their own identification. The absence of dark crystals in a photograph does not establish an inclusion-free interior.
Open source
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