Pyrite Cluster with UV Reactive Sphalerite – Peru

Weight: 139 g
Size: approx. 6 cm × 5.5 cm × 4 cm
Origin: Peru
Display stand: not included

About This Specimen

This is a sculptural multi-generation pyrite crystal cluster displaying sharp metallic cubic faces partially coated in a fine granular sulfide layer. Under UV light the specimen produces vivid orange-red fluorescence across the darker matrix areas, creating a dramatic contrast against the reflective gold crystal surfaces.

The piece formed in at least two distinct mineralisation stages. First, well-defined pyrite crystals grew freely within an open hydrothermal cavity, producing the geometric cubic habit typical of slow, stable growth conditions. Later, a second phase deposited micro-crystalline sulfides over parts of the earlier crystal faces, leaving sections exposed while others became textured and darkened.

Because of this, the specimen shows both reflective mirror-like faces and granular mineral growth in a single piece — effectively recording different chemical environments within the same cavity over time.

In daylight it appears architectural and metallic.
Under UV it becomes active and luminous.

Geological Formation

Pyrite forms in hydrothermal veins when iron-rich fluids circulate through fractures in host rock and crystallise as temperatures and pressures change.

Formation sequence visible here:

1. Open cavity allowed free-growing cubic pyrite crystals

2. Chemical conditions shifted within the fluid

3. Secondary sulfide minerals (including sphalerite-type coatings) deposited over earlier growth

4. Hydrocarbon residues became trapped within the later mineral layer

These trapped organic compounds are responsible for the UV fluorescence — not the pyrite itself, but materials introduced during later mineralisation.

This makes the specimen a record of changing geochemistry rather than a single growth event.

Approximate Geological Age

These hydrothermal sulfide deposits formed during Andean mountain building in the Miocene epoch.

Estimated age: approximately 10–20 million years old

This is significantly younger than many quartz geode systems, forming during active tectonic uplift rather than ancient volcanic cooling.

UV & Visual Notes

• Bright orange-red fluorescence under longwave UV
• Metallic reflective pyrite faces remain non-fluorescent
• Strong contrast between crystal faces and matrix
• Visible multi-stage mineral growth
• Different appearance in daylight vs UV environments

Rarity & Collectability

Pyrite itself is common — sculptural hydrothermal growth sequences are not.

What elevates this specimen:

• Multi-generation crystal formation
• Secondary mineral overgrowth preserved
• UV reactive hydrocarbon inclusions
• Balanced cabinet display form
• Peruvian hydrothermal locality material

Collector category: Cabinet mineral specimen
Rarity rating: ★★★☆☆ (Formation interest rather than rare species)

This type of piece appeals to collectors who value formation history and optical behaviour rather than size alone.

Condition

• Natural unpolished specimen
• Minor contacts typical of 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 pyrite specimens are purely reflective.

This one is interactive.

It preserves a chemical transition inside a mineral vein — from clean metallic crystal growth to later mineral coating — and UV light reveals the final stage of that process. The specimen changes character depending on how it is viewed, making it both geological record and visual display.

You will receive the exact specimen shown.