Blue John (also known as Derbyshire Spar) is a semi-precious mineral, a rare form of fluorite with bands of a purple-blue or yellowish colour. In the United Kingdom it is found only at Blue John Cavern and Treak Cliff Cavern at Castleton in Derbyshire.

2024年7月1日 · Blue John is a rare and highly valued mineral found only in the Blue John Cavern and Treak Cliff Cavern in Castleton, Derbyshire, England. It is a form of fluorspar, a halide mineral composed of calcium fluoride (CaF2), often with impurities that give it its distinctive bands of colors, ranging from purples and blues to yellows and browns.

Visit gemdat.org for gemological information about Blue John. No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care. Please feel free to link to this page.

The cavern takes its name from the semi-precious mineral Blue John, which is still mined in small amounts outside the tourist season and made locally into jewellery. The deposit itself is about 250 million years old.

Blue John Fluorite is a semi-precious mineral with the chemical formula CaF2. Also called Derbyshire Spar, it’s a very rare form of fluorite. It formed during the late Carboniferous and Early Permian periods, when limestones sat at a depth of 1.9 miles (3 kilometers).

2016年9月8日 · The name of this distinctive material is thought to have come from the French “bleu et jaune”, referring to its blue and yellow colours. Blue John is mined from only two places – Treak Cliff Cavern and Blue John Cavern in Castleton.

2023年6月19日 · Unique Geological Formation: Blue John is a rare type of fluorite mineral that is found only in the Castleton area of the Peak District National Park in Derbyshire, England. It forms in the veins and cavities of the local limestone, resulting in its beautiful banding patterns.

The first new vein of the rare mineral Blue John to be discovered in 150 years has been found by accident. The mineral, also known as Derbyshire spar, was found in the Peak District by miner Gary Ridley while he was testing a new stone chainsaw.

2021年3月23日 · Blue John is a unique variety of blue-purple banded fluorite. Hydrocarbons or oils have been deposited on some of the crystal surfaces while the mineral was forming. These oil layers are partly responsible for giving the stone an alternate blue and white banding, best seen when the stone is cut in section.

Blue John (also known as Derbyshire Spar) is a semi-precious mineral, a rare form of fluorite with bands of a purple-blue or yellowish colour. In the United Kingdom it is found only at Blue John Cavern and Treak Cliff Cavern at Castleton in Derbyshire.