Microscopic hematite inclusions have been reported to cause pink quartz.. Cr has been reported to cause the red color in spinels and Fe+3 causes the brown color in spinels. read more
Calcite also shows a variety of colors including green that is due to Cu acording to researchers, blue calcite has been reported to be due to the Fe+2 and Fe+3 contents. and pink calcite has been reported to be due to cobalt content. read more
Blue calcite, 38K; Natural radiation interacts with sheared calcite to produce blue colors. An interesting experiment is to break a colorless calcite crystal into chips up to 3 mm in size. When some of the are chips are exposed to ionizing radiation (such as gamma-rays) they turn amber colored. read more