Description
Grandidierite – Natural Mineral Specimen from USA (9–12mm)
This Grandidierite specimen from the USA is a genuine natural mineral example, carefully selected for its distinctive blue-green colour and collector appeal. Measuring approximately 9–12mm (full sizing please see photo), each piece is a carefully chosen specimen. The photograph provided shows an example of the actual mineral you will receive. Every item includes a Certificate of Authenticity lifetime guarantee generic card, confirming it as a genuine mineral specimen.
Mineral Species & Chemical Composition
Grandidierite is a rare magnesium iron aluminium borosilicate mineral with the chemical formula:
(Mg,Fe)Al₃(BO₃)(SiO₄)O₂
It crystallises in the orthorhombic crystal system and is known for its pleochroic properties, meaning it can display different shades when viewed from different angles. Depending on orientation, grandidierite may show blue, green, or bluish-green tones.
With a hardness of approximately 7–7.5 on the Mohs scale, grandidierite is a relatively durable mineral. Well-formed crystals are uncommon, and many specimens occur as granular or irregular crystal fragments within host rock.
Colour, Optical Properties & Crystal Characteristics
Grandidierite is admired for its rich, oceanic colour range, which may include:
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Teal blue
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Deep green
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Blue-green tones
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Subtle colour zoning
One of its most notable features is pleochroism, where the colour intensity changes depending on viewing direction due to its internal crystal structure.
This 9–12mm specimen may display:
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Semi-translucent to opaque body
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Natural crystal faces or irregular growth
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Vitreous to slightly silky lustre
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Subtle internal inclusions
Each piece is unique in shape, surface texture, and colour saturation, reflecting its natural geological formation.
Geological Formation & USA Locality Context
Grandidierite forms in high-grade metamorphic environments, often associated with boron-rich geological settings. It may develop within:
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Metamorphosed aluminium-rich rocks
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Contact metamorphic zones
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Boron-bearing mineral assemblages
The mineral forms under conditions of elevated temperature and pressure, where magnesium, iron, aluminium, boron, and silica combine during metamorphic processes.
Although Madagascar is the classic locality for grandidierite, occurrences in the USA are rare and add locality interest for collectors seeking unusual mineral species from American deposits.
Associated minerals in grandidierite-bearing environments may include sillimanite, spinel, tourmaline, and other borosilicates depending on the specific geological context.
Size, Presentation & Authenticity
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Mineral: Grandidierite
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Chemical Formula: (Mg,Fe)Al₃(BO₃)(SiO₄)O₂
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Crystal System: Orthorhombic
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Origin: USA
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Size: Approximately 9–12mm (please refer to photo for full sizing reference)
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Authenticity: Includes Certificate of Authenticity lifetime guarantee generic card
This compact specimen is ideal for collectors of rare minerals, micromount enthusiasts, educational geology collections, or as a unique natural history gift. Its rarity and distinctive colour make it a standout addition to any mineral cabinet.
Collecting & Traditional Associations
Grandidierite is considered one of the rarer collector minerals due to its limited global distribution and distinctive appearance. Specimens from less common localities, such as the USA, are especially appealing to collectors focused on geographic diversity.
In spiritual traditions, grandidierite is traditionally associated with clarity and harmony; these interpretations are cultural rather than scientific. From a mineralogical perspective, its appeal lies in its borosilicate chemistry, orthorhombic crystal structure, and striking pleochroic colour.
A genuine Grandidierite specimen from the USA, carefully chosen for quality and supplied with certificate of authenticity, offering rare mineral interest in a collectible 9–12mm size.
