Opal Gunheath China Clay Pit Cornwall UK Natural Silica Mineral Specimen
£ 540.00
GENUINE OPAL – GUNHEATH CHINA CLAY PIT, STENALEES, TREVERBYN, CORNWALLThis natural Opal specimen from Gunheath China Clay Pit, Stenalees, Treverbyn,
Cornwall, England, UK, is a genuine and carefully selected British mineral. The photograph provided shows the exact specimen you will receive. Please refer to the images for full sizing and scale details.This crystal includes a fully hand-signed Premium Certificate of Authenticity confirming its genuine origin and documented Cornish provenance. MINERAL SPECIES & CLASSIFICATIONOpal is a hydrated amorphous form of silica with the chemical composition SiO₂·nH₂O. Unlike quartz, which has a well-ordered crystal lattice, opal lacks long-range crystalline structure and is therefore classified as a mineraloid.Mineral Name: OpalChemical Formula: SiO₂·nH₂OMineral Group: Silica mineraloidCrystal System: AmorphousHardness: 5.5–6.5 on the Mohs scaleLustre: Vitreous to waxyTransparency: Opaque to translucentCornish opal from china clay deposits is typically common opal rather than precious opal. It may display milky white, cream, pale blue or soft grey tones depending on silica concentration, water content and trace elements present during formation. GEOLOGICAL SETTING – ST AUSTELL GRANITE & CHINA CLAY DISTRICTGunheath China Clay Pit lies within the St Austell Granite complex, part of the Cornubian Batholith emplaced during late Carboniferous to early Permian tectonic activity. The granite underwent extensive hydrothermal alteration, creating one of the most important china clay producing regions in the world.China clay (kaolin) forms through the chemical alteration of feldspar-rich granite by circulating mineral-rich fluids. During this process, silica is mobilised and redeposited within fractures, cavities and altered zones of the host rock.Opal forms as a secondary silica deposit when silica-rich fluids precipitate in open spaces under low-temperature conditions. The geological environment includes:
• Granite intrusion and cooling fractures
• Hydrothermal alteration and kaolinisation
• Secondary silica infill within joints and cavities
• Long-term weathering processesAssociated minerals from the Gunheath district may include:
• Kaolinite
• Quartz
• Tourmaline
• Fluorite
• MicaThis geological context gives Cornish opal a strong connection to the historic china clay industry of Treverbyn and the wider St Austell region. PHYSICAL CHARACTERISTICS & NATURAL FEATURESThis specimen may display:
• Massive or botryoidal silica growth
• Smooth, waxy to glassy surfaces
• Subtle translucency at thinner edges
• Natural granite or clay matrix attachmentBecause opal is amorphous, it does not form distinct crystal faces. Instead, it develops as nodular masses, vein fillings or layered silica deposits within fractures. Surface texture and colour variation reflect natural geological processes rather than artificial treatment.Minor inclusions or matrix remnants are natural features that enhance authenticity and locality character. COLLECTIBILITY & CORNISH PROVENANCECornwall is internationally recognised for its diverse mineralogy and rich mining heritage. Opal from named china clay pits such as Gunheath is comparatively uncommon and desirable among collectors of British minerals.Collectors value this material for:
• Documented St Austell Granite provenance
• Association with historic china clay workings
• Secondary silica mineral formation
• Recognised Cornwall localitySpecimens from Gunheath China Clay Pit represent a tangible link to one of Cornwall’s most significant geological and industrial districts. AUTHENTICITY & PRESENTATIONThis Opal specimen has been carefully chosen for its natural character and regional geological importance. The image shown is of the exact specimen you will receive.Included with your purchase is a fully hand-signed Premium Certificate of Authenticity confirming this is a genuine Opal specimen from Gunheath China Clay Pit, Stenalees, Treverbyn, Cornwall, England, UK.A distinctive example of Cornish silica mineralisation, this piece combines documented locality, geological significance and natural mineral beauty in one authentic British specimen.
Cornwall, England, UK, is a genuine and carefully selected British mineral. The photograph provided shows the exact specimen you will receive. Please refer to the images for full sizing and scale details.This crystal includes a fully hand-signed Premium Certificate of Authenticity confirming its genuine origin and documented Cornish provenance. MINERAL SPECIES & CLASSIFICATIONOpal is a hydrated amorphous form of silica with the chemical composition SiO₂·nH₂O. Unlike quartz, which has a well-ordered crystal lattice, opal lacks long-range crystalline structure and is therefore classified as a mineraloid.Mineral Name: OpalChemical Formula: SiO₂·nH₂OMineral Group: Silica mineraloidCrystal System: AmorphousHardness: 5.5–6.5 on the Mohs scaleLustre: Vitreous to waxyTransparency: Opaque to translucentCornish opal from china clay deposits is typically common opal rather than precious opal. It may display milky white, cream, pale blue or soft grey tones depending on silica concentration, water content and trace elements present during formation. GEOLOGICAL SETTING – ST AUSTELL GRANITE & CHINA CLAY DISTRICTGunheath China Clay Pit lies within the St Austell Granite complex, part of the Cornubian Batholith emplaced during late Carboniferous to early Permian tectonic activity. The granite underwent extensive hydrothermal alteration, creating one of the most important china clay producing regions in the world.China clay (kaolin) forms through the chemical alteration of feldspar-rich granite by circulating mineral-rich fluids. During this process, silica is mobilised and redeposited within fractures, cavities and altered zones of the host rock.Opal forms as a secondary silica deposit when silica-rich fluids precipitate in open spaces under low-temperature conditions. The geological environment includes:
• Granite intrusion and cooling fractures
• Hydrothermal alteration and kaolinisation
• Secondary silica infill within joints and cavities
• Long-term weathering processesAssociated minerals from the Gunheath district may include:
• Kaolinite
• Quartz
• Tourmaline
• Fluorite
• MicaThis geological context gives Cornish opal a strong connection to the historic china clay industry of Treverbyn and the wider St Austell region. PHYSICAL CHARACTERISTICS & NATURAL FEATURESThis specimen may display:
• Massive or botryoidal silica growth
• Smooth, waxy to glassy surfaces
• Subtle translucency at thinner edges
• Natural granite or clay matrix attachmentBecause opal is amorphous, it does not form distinct crystal faces. Instead, it develops as nodular masses, vein fillings or layered silica deposits within fractures. Surface texture and colour variation reflect natural geological processes rather than artificial treatment.Minor inclusions or matrix remnants are natural features that enhance authenticity and locality character. COLLECTIBILITY & CORNISH PROVENANCECornwall is internationally recognised for its diverse mineralogy and rich mining heritage. Opal from named china clay pits such as Gunheath is comparatively uncommon and desirable among collectors of British minerals.Collectors value this material for:
• Documented St Austell Granite provenance
• Association with historic china clay workings
• Secondary silica mineral formation
• Recognised Cornwall localitySpecimens from Gunheath China Clay Pit represent a tangible link to one of Cornwall’s most significant geological and industrial districts. AUTHENTICITY & PRESENTATIONThis Opal specimen has been carefully chosen for its natural character and regional geological importance. The image shown is of the exact specimen you will receive.Included with your purchase is a fully hand-signed Premium Certificate of Authenticity confirming this is a genuine Opal specimen from Gunheath China Clay Pit, Stenalees, Treverbyn, Cornwall, England, UK.A distinctive example of Cornish silica mineralisation, this piece combines documented locality, geological significance and natural mineral beauty in one authentic British specimen.
Other Products
