Blue John

Q: What is Blue John?

Blue John is a rare, banded variety of fluorite found exclusively in Blue John Cavern and Treak Cliff Cavern in Castleton, Derbyshire, England. Its characteristic purple and yellow-cream banding, unique among fluorite varieties worldwide, has been carved into vases and ornaments since Roman times an

Q: What is the hardness of Blue John?

Blue John has a Mohs hardness of 4.0, making it relatively soft for use in jewelry.

Q: What color is Blue John?

Blue John is primarily Various.

Q: How much does Blue John cost?

Blue John falls into the Budget (< $50/ct) price range. Prices vary based on color, clarity, cut, and origin.

Q: What is the crystal system of Blue John?

Blue John belongs to the Isometric crystal system.

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Physical & Optical Properties

Category Semi-Precious Gems

Mohs Hardness 4.0

Specific Gravity 3.0 – 3.25

Refractive Index 1.432 – 1.436

Crystal System Isometric

Luster Vitreous

Cleavage Perfect

Color various

Mohs Hardness

Mohs Hardness: 4.0

1 Soft10 Hard

Crystal System

Value & Market

Price Tier Budget (< $50/ct)

Where to Buy Blue John

Blue Nile Fine jewelry retailer

James Allen Gemstone jewelry

Brilliant Earth Ethically sourced gems

Amazon Wide selection

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Treatments

4Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) 3.00 to 3.25Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) PerfectHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) 1.432 to 1.436Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) IsotropicUlrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) Banded white/purpleGemdat.org, Management Team (2012) Transparent,TranslucentArthur Thomas, Gemstones (2009) VitreousArthur Thomas, Gemstones (2009) IsometricHerve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) Cubic, massiveArthur Thomas, Gemstones (2009) Blue John information at mindat.org UK  [www.thamesvalleyminerals.com] Fluorite: The Collector's Choice. Extra Lapis English No. 9

About Blue John

Blue John is a rare, banded variety of fluorite found exclusively in Blue John Cavern and Treak Cliff Cavern in Castleton, Derbyshire, England. Its characteristic purple and yellow-cream banding, unique among fluorite varieties worldwide, has been carved into vases and ornaments since Roman times and remains a protected regional treasure today. Only a few tons of rough Blue John are extracted each year, keeping it perpetually scarce and collectable.