- [l] Related: [[2022-02-21 Toxins]] - ["] Although this common arsenic sulfide mineral occurs worldwide, cut gem-quality realgar is extremely rare. This fine, red stone is very fragile, difficult to cut, and nearly impossible to wear. - [b] [Intro to the oranges](http://www.webexhibits.org/pigments/intro/oranges.html) * ["] The pure orange pigments realgar and chrome orange were favored by the Impressionists. Less pure tones of orange were found largely in the ochre family and lately in the cadmium family. Cadmium orange is a popular color in oils, acrylics, and watercolors. The more recently developed Azo orange is cheaper than cadmium orange, is non-toxic, and retains the same degree of lightfastness. - [b] [Wikipedia](https://en.wikipedia.org/wiki/Realgar) * ["] Realgar (/riˈælɡɑːr, -ɡər/ ree-AL-gar, -⁠gər), also known as "ruby sulphur" or "ruby of arsenic", is an arsenic sulfide mineral. It is a soft, sectile mineral occurring in monoclinic crystals, or in granular, compact, or powdery form, often in association with the related mineral, orpiment (As2S3). It is orange-red in color, melts at 320 °C, and burns with a bluish flame releasing fumes of arsenic and sulfur. Realgar is soft with a Mohs hardness of 1.5 to 2. * ["] After a long period of exposure to light, realgar changes form to a yellow powder known as pararealgar. It was once thought that this powder was the yellow sulfide orpiment, but is a distinct chemical compound.