Colors from metal ions in minerals

All of the examples of colored minerals on this page have color due to metal ions.  Ions of the first row transition elements (Ti to Cu) are normally responsible for color in these minerals.  These ions have electrons in the five 3d orbitals. In the crystallographic sites found in minerals, the 3d orbitals split into different energies. Visible light interacts with these electrons and causes them to be excited to higher energy orbitals. The wavelengths that cause these transitions are subtracted from the incident light resulting in color.

First Row Metals

• Ca²⁺, Sc³⁺, and Ti⁴⁺ by themselves all cause no color in minerals. They have no electrons in d-orbitals. Titanium can interact with other metal ions to cause color as discussed in the section on intervalence charge transfer.
• Ti³⁺ by itself is not a factor in the coloration of most terrestrial minerals. Through intervalence charge transfer and band gap process it can contribute to the color of a few extraterrestrial minerals such as hibbonite and pyroxene and the rare blue examples of the terrestrial TiO₂ minerals, anatase and rutile. Chains of edge-sharing octahedra in Ti³⁺ - Ti⁴⁺-bearing clinopyroxene from the Allende meteorite give rise to a olive-green color. Originally it was argued by Dowty and Clark (1973) that features from both Ti³⁺ and Ti³⁺ - Ti⁴⁺ intervalence charge transfer contribute to the color, although later Burns (1973) argued that only Ti³⁺ was responsible for the color.
• V³⁺ in grossular garnet (tsavorite variety from Kenya) causes the green color.  In zoisite (tanzanite variety) it contributes to the color which varies depending upon the direction in which you view the crystal (pleochroism).
• VO²⁺ causes bright blue color in a few minerals. Cavansite from India shows the typical blue color of this ion.  Synthetic clinopyroxene grown from lithium vanadate flux can commonly incorporate this ion and cause blue color.  In apophyllite the color is more green than blue.
• Cr³⁺ causes red and green colors. Cr³⁺ causes green color in emerald, synthetic orthopyroxene and jadeite.  Red color from Cr³⁺ is seen in   spinel from Burma and synthetic ruby.
• Mn³⁺ causes red and green colors in octahedral sites. Muscovite mica from Brazil containing is red as is Mn³⁺ in beryl from Utah, synthetic orthopyroxene, and piemontite from Whitewater, California. Andalusite containing Mn³⁺ is green. In the amphibole, tremolite, from New York, it produces a violet color.
• Mn²⁺ usually results in a pink color in octahedral sites. Rhodonite from Minas Gerais, Brazil, is a pyroxenoid containing Mn²⁺and has the typical pink color of Mn²⁺ minerals. Rhodocrosite from Colorado has a high concentration of Mn²⁺ and a bright red color. At lower concentrations, Mn²⁺ causes pale pink color.  When the Mn²⁺ is in a tetrahedral site, then yellow-green color results such as is the case with willemite.
• Fe²⁺ in forsterite from San Carlos, Arizona, and in phosphophyllite from Bolivia is the ion responsible for the green color. In some minerals with high concentrations of Fe²⁺, such as fayalite or orthopyroxene, the color is brown.
• Fe²⁺ in the square planar site of gillespite or eudialyte produces a rasberry red color.
• Fe²⁺ in the eight-coordinated site of pyrope garnet from Tanzania produces the near-red color.
• Fe³⁺ in octahedral sites causes only pale color when the Fe³⁺ ions are isolated from each other by intervening silicate ions, etc. Pale purple color is found in phosphates such as strengite and sulfates such as coquimbite. Yellow-green can be found in ferric silicates such as andradite garnet from Italy.
• Fe³⁺ is in the tetrahedral site of plagioclase feldspar from Lake County, Oregon, produces a pale yellow color. In an unusual variety of diopside containing Fe³⁺ in a tetrahedral site, it produces bright orange color in thin section.
• Co²⁺ in synthetic olivine and cobaltian calcite from the Kakanda Mine, Zaire, causes a typical reddish color. In tetrahedral sites, Co²⁺ causes blue color such is found in some spinels.
• Ni²⁺ in synthetic olivine has the green color typical of Ni²⁺ in an octahedral site. If all the nickel is forced in to the larger M2 site by appropriate chemical substitution (in this case in a LiScSiO₄ olivine), the color is yellow, typical of Ni²⁺ in large, distorted sites.
• Cu²⁺ usually occupies sites distorted from octahedral geometry. It produces blue and green color in minerals such as azurite, malachite, aurichalcite and the blue elbaite tourmaline from Paraiba, Brazil.

Other Metal Ions

• Rare-earth elements (Ce, Pr, Nd) are occasionally factors in the color of minerals. They have narrow lines in the absorption spectra when they are in the normal 3+ oxidation state. Minerals with abundant rare earths often have brown to orange-brown colors. Rare earths can be seen in the spectra of many minerals.

The rare-earth elements have distinctive colors in the 3+ oxidation state and distinctive absorption spectra that change little with different hosts. Here are some examples of synthetic rare-earth garnets and phosphates.

Several of the garnets illustrated show evidence of contamination by other rare-earths - better examples to come in the future

• The UO₂²⁺ ion is responsible for the brilliant yellow color of many uranium minerals such as carnotite and autinite.
• U⁴⁺ gives blue color to zircon.

Often asked questions about color in minerals

• What about lithium?  It is widely believed that Li causes various colors in minerals. Li⁺  does not cause color; it has no electrons in the d-orbitals.  It frequently accompanies other ions such as Mn which do cause color.
• What about cesium?  It is widely believed that Cs causes various colors in minerals. Cs⁺  does not cause color; it also has no electrons in d-orbitals.  It frequently accompanies other ions such as Mn which do cause color.

Back to the list of causes of color

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last updated: 30-Apr-2006