Rose Quartz (#15)
|South America||Lavra da Ilha, Minas Gerais, Brazil||2" x 1 ¾" x 1 ¼"|
These well-formed crystals of rose (that is, pink) quartz are comparatively rare and differ from the much more common massive rose quartz that does not display crystal form. This quartz from Minas Gerais, Brazil owes its color to a color center, as with specimens 4 and 9 in this display. A small amount of the Si is replaced by aluminum (Al) and phosphorus (P), and it is subjected to natu ral radiation from the surrounding rocks. This ionizes some O2- to O- + e- (a free electron). That electron, interacting with light, produces the pink color.
The more common massive rose quartz contains submicroscopic inclusions of a mineral containing Al that is accompanied by small amounts of impurities - iron (Fe2+) and titanium (Ti4+). Some of these Fe and Ti ions are nearby each other, and when a photon strikes an Fe2+, it may "knock" an electron to a nearby Ti4+. The following reaction occurs:
Fe2+ + Ti4 → Fe3+ + Ti3+
The energy for this electron transfer comes from the short wavelength (high energy) part of the spectrum, and those wavelengths are thus lost from the spectrum. What is left - what you see - is light at the long wavelength end of the spectrum: red. There are very few Fe and Ti atoms close together, so the color is not intense. This phenomenon is called charge transfer, and it is responsible for the color in many minerals.