Opal Goonbarrow China Clay Pit Cornwall Genuine Mineral Specimen with Certificate of Authenticity

Genuine Opal – Goonbarrow China Clay Pit, Bugle, Cornwall, UK

This Opal specimen from Goonbarrow China Clay Pit, Bugle, Treverbyn, Cornwall, England, UK, is a genuine and carefully selected example of Cornish silica mineralisation. The photograph provided shows the exact specimen you will receive. Please refer to the images for full sizing details and accurate scale.

This crystal includes a Certificate of Authenticity lifetime guarantee generic card confirming its genuine origin and locality.

Mineral & Geological Classification – Opal

Opal is a hydrated amorphous form of silica with the chemical composition SiO₂·nH₂O. Unlike crystalline quartz, opal does not possess a regular crystal lattice and is classified as a mineraloid rather than a true crystalline mineral.

Mineral Name: Opal
Chemical Composition: Hydrated Silicon Dioxide
Mineral Group: Silica (Mineraloid)
Crystal System: Amorphous
Hardness: 5–6 on the Mohs scale
Lustre: Vitreous to waxy
Transparency: Translucent to opaque

Cornish opal from china clay districts typically occurs as common opal rather than precious opal. It may display milky white, cream, pale blue or subtle earthy tones depending on trace elements and formation conditions. Surfaces can range from smooth and waxy to botryoidal or vein-filling textures.

Geological Setting – Goonbarrow China Clay Pit

Goonbarrow China Clay Pit lies within the St Austell granite district, part of the Cornubian Batholith formed during the late Carboniferous to early Permian periods. The intrusion of granite generated hydrothermal systems and subsequent deep chemical weathering processes.

The decomposition of feldspar-rich granite produced kaolin (china clay), for which the region is internationally known. During hydrothermal alteration and later supergene processes, silica-rich fluids circulated through fractures and cavities in the decomposed granite. As these fluids cooled and evaporated, opal precipitated within voids and along fracture planes.

This environment is characterised by:

• Granite-hosted hydrothermal activity

• Intense chemical weathering

• Silica mobilisation and redeposition

Associated minerals in similar china clay settings may include quartz, kaolinite, fluorite, tourmaline and secondary copper minerals depending on local geochemistry.

Physical Characteristics & Notable Traits

This specimen may display:

• Milky or translucent opal masses

• Vein-like or nodular formation within matrix

• Waxy to vitreous surface lustre

• Natural surface texture and silica banding

Opal from Goonbarrow often occurs as seam fillings or irregular masses within altered granite. The lack of crystalline structure gives it a smooth, compact appearance distinct from quartz.

Natural colour variation, minor inclusions and matrix attachment are part of the mineral’s geological history and confirm authenticity.

Geological Importance & Collectibility

Cornwall is globally recognised for its granite-related mineralisation and historic china clay industry. Opal from documented china clay pits such as Goonbarrow represents secondary silica deposition within a granite-hosted alteration system.

Specimens from named Cornish localities are valued by collectors for their documented provenance and regional geological significance. This piece is suitable for mineral cabinets, educational geological collections and collectors of British locality minerals.

Because this is a genuine natural specimen, it displays unique structural and surface characteristics shaped by its formation environment. The photograph shows the exact specimen you will receive.

Authenticity & Presentation

This Opal specimen from Goonbarrow China Clay Pit has been carefully chosen for quality and locality significance. Included with your purchase is a Certificate of Authenticity lifetime guarantee generic card confirming its genuine origin from Bugle, Treverbyn, Cornwall, England, UK.

Combining classic granite-hosted silica deposition with documented Cornish provenance, this specimen offers mineral authenticity, geological interest and strong collector appeal in one carefully selected piece.