Kaholong

Kaholong is a milky-white variety of fine opal, which has been one of the favoured precious gemstones for many centuries. The group of fine opals includes quite a number of wonderful gemstones, which share one characteristic: they shine and sparkle in a continually changing play of colours called "opalising". In order to best bring out the play of colour in a fine opal, the stones are cut and polished to round or oval cabochons, or any other softly domed shape, depending on the raw material. Only the best qualities of fire opal, however, are suited to faceting.

Milky opal or Kaholong emits an exceptionally soft shine. It was highly valued in ancient India for its pure whiteness, which is also the reason why kaholong was called 'solid milk of sacred cow'. The Buddhists associate kaholong with lotus, a symbol of pure soul.

The name Opal was probably derived from Sanskrit “upalo“, meaning ”valuable stone“. This was probably the root for the Greek term “opallios”, which translates as “colour change”. In the days of Roman antiquity there existed a so-called “opalus”, or a “stone from several elements”. Pliny, the famous Roman author, was the first to describe opal as a gemstone which combines the best possible characteristics of the most beautiful of gemstones.

Up to the first half of the 19th century, opals were relatively rare. Almost ninety-five per cent of all fine opals come from the dry and remote outback deserts of Australia. The history of Australian Opal began actually millions of years ago, when parts of Australia were covered by a vast inland sea, and stone sediment was deposited along its shoreline. When the water masses flooded back, they flushed water containing silica into the resulting cavities and niches in the sedimentary rocks, and also the remains of plants and animals were deposited there. Slowly the silica stone transformed into opal, for basically opals are simply a combination of silica and water. Other occurrences of opal were discovered in Mexico , Brasil , Russia , India , USA to mention just the most notable occurrences.

Opals are amorphous crystals of hydrated silicon dioxide where the water content can reach up to 8 %. The precious opal stones are brittle, heat sensitive and break and scratch easily. Generally opals do not show any crystalline X-ray diffraction pattern, signifying that they are structurally amorphous.

Opal is often found as flat lenses, or thin layers, bigger pieces are rather rare. If you leave a thin but supporting layer of the harder mother rock, you will receive a pre-stage of the opal-doublets which are frequently used today for mass produced jewellery. These are gemstone combinations consisting of a surface of a thin opal plate, which has been mounted on onyx, obsidian or artificial black glass. Triplets have been developed from this design, where the opal layer receives an additional cover from rock crystal, plastic, hard glass or lead glass for protection.

Characteristics:

Chemistry: SiO₂nH₂O

Hardness (Mohs scale): 5.5 – 6.5

Density: 1.98 – 2.25

Refractive index: 1.44 – 1.47

Dispersion: weak

Crystal system: amorphous

Cleavage: none

Fracture: conchoidal

Transparency: translucent to opaque

Luster: vitreous, dull