Cuprorivaite

Egyptian Blue, was invented in Egypt and has been known since the middle of the 3rd millennium BC. Egyptian Blue was the first artificially produced pigment known to humankind. It was used as early as the Late Bronze Age (16th–12th century BC), even far beyond Egypt.
Initially, the popular blue pigment was used extensively in Egypt and the Middle East as a component to produce small objects such as beads, statuettes, scarabs and inlays. It was used almost continuously from its first appearance until Roman times. Besides Egypt and the Middle East, the pigment was also used in Minoan (pre-Greek culture) Crete and in the Roman world. During the Roman Empire (8th century BC to 7th century AD), the pigment Egyptian Blue continued to be highly valued and spread from Britain to North Africa and was also used in Asia Minor.
Egyptian Blue was used in antiquity as a pigment for paintings on various surfaces such as wood, paper, stone, ceramics, lime plaster and gypsum. It was also used as a colorant in glass and faience. It is even said to have been sought after as eye shadow (make-up) by women in antiquity. Archaeological evidence suggests that the demand for Egyptian Blue increased greatly as the need for pigments for wall paintings increased during the Hellenistic and Roman periods. After the fall of the Roman Empire, the use of Egyptian Blue declined, except in a few areas; there is still some documentation, especially from the Byzantine world (late antiquity). Later, the coveted pigment found its way into medieval wall painting, as well as into the masterpieces of Italian Renaissance painting. The technological knowledge on which the production of the blue pigment was based was presumably lost at the end of the first millennium AD and was only rediscovered in the decades around 1900. It is possible that the use of Egyptian Blue in the post-Roman period was a recycling of lumps produced in the Roman period.

The first hydrothermal synthesis of CaCuSi4O10 as micron-scale clusters of thin platelets, distinct from morphologies generated under salt-flux or solid-state conditions. The hydrothermal reaction conditions are surprisingly specific: too cold, and instead of Ca-CuSi4O10, a porous calcium copper silicate forms; too hot, and calcium silicate (CaSiO3) forms. The precursors also strongly impact the course of the reaction, with the most common side product being sodium copper silicate (Na2CuSi4O10). Optimized conditions for hydrothermal Ca- CuSi4O10 formation from calcium chloride, copper(II) nitrate, sodium silicate, and ammonium hydroxide are 350 °C at 3000 psi for 72 h; at longer reaction times, competitive delamination and exfoliation causes crystal fragmentation. These results illustrate that CaCuSi4O10 is an even more unique material than previously appreciated.

The narrow conditions that it forms under hydrothermal conditions indicate that natural occurrences will be rare.