Chalcedony
Characteristics
- Habit -
- Form - hexagonal or trigonal
- Hardness - 7 (hard)
- Cleavage - none
- Fracture - uneven
- Streak - white
- Lustre - waxy to dull
- Colour - purple, brown, colourless, white, pink
Introduction
Variety of microcrystalline quartz. May have been named after an ancient port in Turkey 'Khalkedon', where there were exptensive depositis of this mineral. White when pure. May contian microscopic inclusions of other minerals which give it colour. Many varieties are gems with their own names. All varieties found worldwide. Forms when silica rich waters at low temperatures percolate through existing rocks.
Ancient use includes Aztec sacrifical blade.
Varieties
Agate
Has distinct banding.
Paul Bunyan plume agate (Rock & Gem, vol.56 no.6, 2026, pp.46-48) - From San Bernardino county, near Fort Irwin; Rich red colour in soft grey or white chalcedony, with distinct bursts of tubes amd wispy forms. Occasional crystals or calcite inclusions. Locked within tough, pink rhyolitic host rock. The locality is no longer open to the public as it is under private claim. Get material at shows or old collections or FB.
Chrysoprase
Coloured greeen by nickel.
Onyx
Straight banding
Carnelian
Orange-red variety of chalcedony (polycrystalline quartz); translucent to opaque; popular for small carvings and engraved seals since antiquity; one of the first gems to be treated - heat treated to intensify the colour from c.4000 years ago.
Most heated or stained material is chalcedony.
Lore: thought to have powers to preserve harmony.
Nomenclature: British English refered to it as 'cornelian'. Name derived from Latin for cornel-berry which can be bright red. 'Carnelian' may originated from a mistaken idea that the name came from the Latin 'carnis' for flesh.
Kambaba Jasper
Kambaba Jasper, also known as Crocodile Jasper or Kambaba Stone, is a unique type of jasper renowned for its striking green and black orbicular patterns. It is a type of sedimentary rock composed primarily of microcrystalline quartz (chalcedony) and is often classified as a stromatolite or fossilized algae due to its distinctive circular patterns resembling algae colonies. Kambaba Jasper is prized for its aesthetic appeal and is widely used in jewelry making, ornamental objects, and spiritual practices due to its purported metaphysical properties.
The green coloration in Kambaba Jasper is attributed to the presence of various minerals, including chlorite and hornblende, while the black orbs are typically composed of other minerals such as pyrite or magnetite. These minerals infiltrate the sedimentary layers, creating the unique patterns observed in the stone. Primary source is Madagascar. (https://geologyscience.com/gemstone/kambaba-jasper/)
Bloodstone
Opaque chalcedony, green jasper speckled with red dots. Silicon dioxide with needle-like inclusions of minerals such as chlorite, actinolite or pyroxene. Red dots are inclusion of iron oxides like hematite. Dots/patches/swirls of colour can be white, yellow, orange, brown and blue. More translucent variety with red spots sometimes called heliotrope - classic bloodstone. More opaque with more uniform green colour and few to no spots are sometimes called plasma.
Most high quality come from India, particularly Gujarat. It often fills fissures and cavities within a matrix rock. The more deep-red or dark orange the higher the price.
Primarily used by lapidaries. Mohs' 6.5-7 and can take a high shine. Isle of Rum bloodstone set into brooches during the Victorian period and inlayed into snuff boxes. Good for carvings. Used by ancient Bablonians to craft seals , cameos and intaglios.
Lore: a birthstone for March. Other names - heliotrope, the Martyr's gem, stone of Babylon, Christ's stone. New Agers wear as a lucky charm. Babylonians used it as a healing stone & to divine the future eg: forcast weather. Romans took into battle for wounds - iron oxide can have a coagulant effect. Gnostics used it to dispel melancholy which was associated with blood disorders.
Arab Roots of Gemolgy
Some elements from 'Arab roots of gemolgy: Ahmad ibn Yusuf Al Tifaschi's Best Thoughts on the Best of Stones' (c.1240) trans. Samar Najm Abul Huda. The Scarecrow Press, London, 1998.
Cornelain
Brought from Yemen mines and Mecca and the shores of the sea of Ruma.
Five varieties:
- red - the best one
- rabi - red with a shade of yellow, next best
- blue
- black
- white - least best
Hot and hard. If the red one is worn asan amulet it stills fear during battle. If rabi, the colour of meat to which salt has been added and showing white banding, is worn in a ring it stops hemorrhage from any part of the body, esp. women with long periods. If any variety is rubbed against teeth it whitens them, removes cavities and prevent bleeding of gums. Calcined cornelian fixes loose teeth.
The red variety and rabi are priced, the others are of no particular value. Used to make knife hilts.
Jasper
Also called Yassb. Is a silver based stone - formed in silver mines from vapours still not condensed into silver.
Brought from Yemen and mostly found as small stones. Comes in white and olive green (the best one). There is a blue variety but it is dyed. It can easily be dyed so jewllers dye it to imitate emerald.
Beneficial for all stomach ailments if hung externally - although Ahmad said this was incorrect and it was nephrite and not jasper.
