Amethyst Rosette (Flower Formation)

Irai, Rio Grande do Sul, Uruguay

22 x 18.5 x 5.5 cm (8⅝ x 7¼ x 2⅛ inches). 612 grams (1.35 lb).

This specimen is a refined and unusually well-preserved example of an amethyst formation unique to the basalt-hosted pockets of Iraí, located in Rio Grande do Sul, Brazil. Unlike the more common geode material from nearby regions, this variety, reminiscent of a blossoming flower, is immediately recognizable by its radial, dish-like crystal growth, forming as singular free-floating rosettes within vesicular cavities of the Paraná volcanic province.

Measuring approximately 8.6 inches in height and remarkably thin, this piece exhibits a nearly perfect radial geometry with a plate-like silhouette. Its slender amethyst crystals radiate outward in a concentric burst, gradually shifting in hue from transparent white to lavender before transitioning to near colorlessness at its tips. This gradation, both subtle and natural, reflects a precise evolution in the geochemical environment during growth, specifically, the progressive enrichment of iron and its subsequent exposure to natural irradiation that produces the amethyst coloration.

The form is concave, lightly domed inward like a bowl or a blossom in bloom—an organic geometry that has become the visual signature of the Iraí material. Most specimens of this type form as matrix-free, suspended growths within pockets, developing as independent radial sprays rather than encrusting substrates. While examples occasionally appear in multiples or perched on matrix, the vast majority, like this one, formed in isolation, allowing complete radial symmetry to develop unimpeded.

The specimen is translucent when held to light, and its slender profile allows for dramatic presentation when backlit. This optical characteristic, combined with the natural symmetry and softly zoned color, makes these pieces especially prized among collectors for both their structural uniqueness and display potential.

Geologically, the crystals formed within vesicular basalt flows of the Serra Geral Formation, part of the Paraná Flood Basalt Province, during the Early Cretaceous, specifically between approximately 136 and 127 million years ago. The isolated, radial growths represent a specialized crystallization mode, likely driven by slow silica-rich fluid influx, ample cavity space, and localized variations in trace elements.

This specimen exemplifies the hallmark characteristics of the Iraí flower formations, standing out for its proportion, translucency, and graceful symmetry—attributes that underscore the geological and aesthetic appeal of this distinctive Brazilian occurrence.

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