Boulder Opal (two parts) of 345g on black base -Australia-

An Australian curiosity: a precious Opal Vein (Opale AG) in its matrix. From Boulder in Queensland, Australia. What was the bottom of a shallow sea in the Cretaceous, became a layer of amber-coloured sandy clay: the matrix of an Opal. The opal is made up of tiny spheres of silica of different sizes that have agglomerated during wet and dry periods. The red reflections come from the largest spheres: 350 nanometers! This piece is therefore composed of even smaller nanospheres. And all these colors are interferences with light due to traces of magnesium, aluminum, arsenic, potassium, uranium... This thin layer is not separated from its matrix when the opal is worked in jewellery: the matrix will be refined and polished. Here it is perfectly natural. We see that the outdoor photos with the sun give more intense colors.