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

Genuine Opal – Gunheath China Clay Pit, Stenalees, Treverbyn, Cornwall

This Opal specimen from Gunheath China Clay Pit, Stenalees, Treverbyn, Cornwall, is a genuine British mineral example carefully selected for its natural character and locality significance. 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 mineral identity.

Mineral & Geological Classification – Opal (Amorphous Silica)

Opal is a hydrated amorphous form of silica with the chemical formula SiO₂·nH₂O. Unlike crystalline quartz, opal does not possess a regular crystal lattice and is therefore classified as a mineraloid rather than a true mineral. Its structure consists of microscopic silica spheres arranged in varying degrees of order, which can influence optical effects.

Mineral Type: Mineraloid (Hydrated Silica)
Chemical Formula: SiO₂·nH₂O
Crystal System: Amorphous (non-crystalline)
Hardness: 5.5–6.5 on the Mohs scale
Lustre: Vitreous to resinous
Transparency: Translucent to opaque

Opal from Cornwall commonly forms as common opal rather than precious opal, though subtle internal colour variation may occur depending on silica sphere arrangement and trace element content.

Cornwall Locality – Gunheath China Clay Pit

Gunheath China Clay Pit lies within the Cornubian granite region of Cornwall, an area famous for its complex mineralogy and historic mining activity. The granitic intrusions in this region formed during the late Carboniferous to early Permian periods and created conditions favourable for hydrothermal mineralisation.

Opal in this locality typically forms in fractures and cavities within kaolinised granite and associated clay deposits. Silica-rich fluids percolating through the altered granite gradually deposited layers of hydrated silica, eventually forming opal masses and seams.

The china clay (kaolin) industry in St Austell and surrounding areas has exposed numerous mineral specimens, including quartz, tourmaline, cassiterite and opal, making the locality well known among British mineral collectors.

Appearance & Notable Traits

Cornish opal often appears in milky white, cream, pale grey or translucent tones, sometimes with subtle internal banding or soft colour variation. The surface may display a smooth, waxy to vitreous lustre when polished, or a natural matte texture if left unpolished.

Because opal contains water within its structure, it may show minor internal fractures or surface patterns that developed naturally during formation. These features are part of the specimen’s geological history and authenticity.

Depending on the silica sphere arrangement, some opal specimens may exhibit a gentle internal glow or faint play of light under certain angles, though this varies by individual piece.

Geological Significance & Collectibility

Opal from Cornwall represents a classic example of hydrothermal silica deposition within a granite-hosted mineral district. The Gunheath China Clay Pit locality adds collector value due to its established geological heritage and association with the wider St Austell granite complex.

British locality specimens are particularly sought after by mineral collectors who appreciate documented provenance and regional mineral diversity. This specimen offers both geological interest and locality significance within the context of Cornish mining history.

Because this is a genuine natural specimen, each piece displays unique texture, structure and tonal variation. The photograph shows the exact opal specimen you will receive.

Authenticity & Presentation

This Opal specimen from Gunheath China Clay Pit has been carefully chosen for authenticity, character and presentation. Included with your purchase is a Certificate of Authenticity lifetime guarantee generic card confirming its genuine origin from Stenalees, Treverbyn, Cornwall.

Combining Cornish granite geology with natural hydrated silica formation, this opal specimen offers documented locality, mineral authenticity and classic British collector appeal in one carefully selected piece.