Kids, did you ever wonder about the color of certain minerals, gems, or birthstones? Gemstones are minerals that can be polished and cut for use as an ornament or jewelry. The color of a gemstone comes from tiny, trace amounts of transition metals present in the main rock or mineral. Transition metals are those in the middle, center section of a periodic table, from scandium (Sc) to zinc (Zn) in the first row. The main rock or mineral is usually a very common material, such as silicon dioxide (silica, SiO2) or aluminum oxide (alumina, Al2O3).
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Take a look at the colors of common gemstones and the metals responsible for their color. You can do this at a store that sells rocks and minerals, or a gem and mineral trade show, or even at a department store jewelry counter.
Amethyst is a colored form of quartz (silica) that gets its purple color from the presence of iron. Aquamarine is a blue variety of the mineral beryl (beryllium aluminum silicate). The pale blue color comes from iron. Emerald is another form of beryl, this time in a green color due to the presence of chromium and sometimes vanadium. Garnet is an aluminosilicate that gets its deep red color from iron. Peridot is the gemstone form of olivine, a magnesium silicate mineral formed in volcanoes. The yellow-green color comes from iron. Have you heard of Hawaii’s green peridot sand beaches?
Ruby is the name given to gemstone-quality corundum (alumina) that is pink to red in color. The color comes from the presence of trace chromium. Corundum that is any color besides red is called sapphire. Blue sapphires are colored by iron and titanium. Turquoise is an opaque mineral, meaning that it is not clear, that gets its blue to green color from copper within its aluminum phosphate matrix.
--------------
Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
November 2010
----------------
References:
Anne Marie Helmenstine, “Gemstone Colors and Transition Metals”, http://chemistry.about.com/od/geochemistry/tp/Gemstone-Colors-And-Transition-Metals.htm?nl=1
Learn About Gemstones
Geochemistry & Petrochemistry
