Opal from Mondulkiri, Cambodia - New Update 2022 - Video

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Cambodian opal

Opal is a hydrated amorphous form of silica (SiO2 nH2O); its water content can vary from 3 to 21% by weight, but is typically 6 to 10%. Due to its amorphous nature, it is classified as a mineraloid, in contrast to the crystalline forms of silica, which are classified as minerals.

It is deposited at a relatively low temperature and can be found in crevices of almost any type of rock, most commonly occurring with limonite, sandstone, rhyolite, marl, and basalt. Opal is the national gemstone of Australia.

The internal structure of the playful color of the opal makes it refract light. Depending on the conditions in which it is made, it can take on many colors. Stones range from clear to white, grey, red, orange, yellow, green, blue, purple, pink, pink, slate, olive, brown and black.

Of these shades, black stones are the rarest, while white and green are the most common. Opals vary in optical density from opaque to translucent.

The opal play of color shows a variable interplay of internal colors and, although a mineraloid, has an internal structure. On a microscopic scale, color-playing opal is composed of silica spheres ranging in diameter from 150 to 300 nm in a dense hexagonal or cubic grid.

JW Sanders demonstrated in the mid-1960s that these ordered quartz spheres produced internal colors by causing interference and diffraction of light passing through the opal microstructure.

The correct size and packaging of these beads determines the quality of the stone. When the distance between regularly stacked planes of the spheres is about half the wavelength of the visible light component, light at that wavelength can be diffracted through the grating formed by the stacked planes.

The observed colors are determined by the distance between the planes and the orientation of the planes with respect to the incident light. This process can be described by the Bragg diffraction law.

Opal from Mondulkiri, Cambodia.

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