Deep Purple Amethyst Cluster With ‘Triceratops Horn’ Calcite Formation. Southern Brazil

Formed within the gas cavities of ancient volcanic rock, this exceptional amethyst specimen represents a moment of mineral convergence, where silica-rich and calcium-bearing solutions crystallised in harmony over millions of years.

The amethyst displays a dense array of sharply terminated crystals, exhibiting a deep, highly saturated violet hue — a result of trace iron impurities and natural irradiation during formation. The crystals are well-defined, with clean terminations and a natural lustre that enhances their structural clarity and visual depth.

Most remarkable is the presence of a distinct calcite formation emerging from within the amethyst matrix. This calcite has developed as a four-sided, triangular structure, rising vertically through the host crystal layer. Its geometry is both unusual and aesthetically striking, creating a sculptural contrast against the darker amethyst backdrop. When led flat, we think the formation bears a notable resemblance to the horn of a Triceratops, lending the specimen a unique, almost prehistoric character.

Such intergrowths indicate a shift in geochemical conditions during formation, where calcite began crystallising after — or alongside — the amethyst, penetrating the existing crystal structure rather than forming independently. This makes the piece not only visually compelling but also geologically informative.

The specimen remains in its natural, unaltered state, preserving its original crystal habit, surface textures, and mineral relationships. It stands as both a decorative centrepiece and a study in mineralogical processes.

Specimen Details

Mineral Composition: Amethyst (Quartz) with Calcite intergrowth

Geological Formation: Secondary mineralisation within volcanic cavity

Locality: Southern Brazil

Dimensions: 110 mm × 83 mm × 50 mm

Calcite Formation Size: Approx. 30 mm × 35 mm (widest points)

Weight: 460 g

Colour: Deep, richly saturated purple

Crystal Habit: Well-terminated prismatic crystals

Transparency: Translucent to semi-transparent

Lustre: Vitreous

Notable Feature: Prominent four-sided triangular calcite formation emerging through amethyst, resembling a Triceratops-like silhouette

Condition: Natural, unpolished, and unrestored specimen