Amethyst with Calcite Rosettes – Artigas, Uruguay (UV Reactive)

Weight: 172 g
Size: approx. 9 cm × 7.5 cm × 5.5 cm
Depth: ~3.5 cm
Origin: Artigas, Uruguay
Display stand: not included

About This Specimen

This is a richly coloured Uruguayan amethyst plate displaying sharp quartz points emerging from a natural agate base, accompanied by perched calcite rosettes that fluoresce brightly under UV light.

The crystal habit is tight and architectural rather than open — a classic feature of Artigas material where slow growth inside basalt cavities produces deep colour saturation and glassy faces instead of large pale points.

Across the crystal surface sit several pale calcite growths, delicately resting on the amethyst tips. These formed after the quartz had already crystallised, recording a second mineralising event inside the geode. Because of this, the specimen captures multiple stages of geological history rather than a single moment of formation.

In daylight it reads as a strong purple display piece.
Under UV it becomes a contrast specimen — dark violet crystal field with floating white luminescent calcite.

Geological Formation

Uruguayan amethyst forms inside volcanic basalt flows.
Gas bubbles trapped in cooling lava create cavities which later fill with silica-rich groundwater.

The formation sequence visible in this specimen:

1. Chalcedony layers deposit first, creating the agate banding base

2. Quartz crystals grow inward, forming amethyst points coloured by trace iron

3. Later fluids re-enter the cavity depositing calcite over the already-formed crystals

This overgrowth relationship is important — it shows the geode reopened after initial crystallisation, making the calcite a secondary mineral phase rather than part of the original growth environment.

The rosette shapes occur because calcite grows along preferred cleavage directions, producing curved layered crystal aggregates instead of sharp prisms.

Approximate Geological Age

The Paraná volcanic province responsible for Uruguay’s amethyst formed during the Early Cretaceous period.

Estimated age: ~130 million years old

These crystals began forming while South America and Africa were still separating as continents.

UV & Visual Notes

• Calcite fluoresces bright white-blue under longwave UV
• Strong contrast against dark amethyst background
• Visible agate banding on matrix edge
• Saturated purple crystal colour typical of Artigas locality
• Attractive triangular natural composition for upright display
• Different appearance in daylight vs UV environments

Rarity & Collectability

Amethyst itself is common — but association pieces are not.

What elevates this specimen:

• Uruguay locality (premium colour locality)
• Secondary mineralisation present
• Fluorescent response
• Clear formation sequence preserved
• Balanced display shape

Collector category: Association specimen
Rarity rating: ★★★☆☆ (Uncommon formation combination rather than rare species)

This is the type collectors move toward after standard geode halves — a piece that explains how a geode formed, not just what it looks like.

Condition

• Natural unpolished specimen
• Minor edge contacts typical of geode extraction
• No repairs or enhancements
• Stable and display ready

Please review photographs carefully as they form part of the description.

Why This Piece Is Special

Many amethysts are decorative.

This one is geological.

It preserves three separate mineral growth events in a single cavity — agate, quartz, then calcite — and the UV response makes that history visible. Instead of just colour, it offers interaction: light changes the story.

Ideal for:
• collectors building a locality cabinet
• UV mineral displays
• educational collections
• anyone who prefers formation over size

You will receive the exact specimen shown.