Dorrite
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Dorrite is a silicate mineral that is isostructural to the aenigmatite group. It is most chemically similar to the mineral rhönite [Ca 2 Mg 5 Ti(Al 2 Si 4 )O 20 ], made distinct by a lack of titanium (Ti) and the presence of Fe 3+ . Dorrite is named for Dr. John (Jack) A. Dorr, a late professor at the University of Michigan that researched in outcrops where dorrite was found in 1982. This mineral is sub-metallic resembling colors of brownish-black, dark brown, to reddish brown.
Dorrite is a silicate mineral that is isostructural to the aenigmatite group. It is most chemically similar to the mineral rhönite [Ca 2 Mg 5 Ti(Al 2 Si 4 )O 20 ], made distinct by a lack of titanium (Ti) and the presence of Fe 3+ . Dorrite is named for Dr. John (Jack) A. Dorr, a late professor at the University of Michigan that researched in outcrops where dorrite was found in 1982. This mineral is sub-metallic resembling colors of brownish-black, dark brown, to reddish brown.
Discovery
Dorrite was first reported in 1982 by A. Havette in a basalt-limestone contact on Réunion Island off of the coast of Africa. The second report of dorrite was made by Franklin Foit and his associates while examining a paralava from the Powder River Basin, Wyoming in 1987. Analyses determined that this newly found mineral was surprisingly similar to the mineral rhönite, lacking Ti but presenting dominant Fe 3+ in its octahedral sites. Other minerals that coexist with this phase are plagioclase, gehlenite-akermanite, magnetite-magnesioferrite-spinel solid solutions, esseneite, nepheline, wollastonite, Ba-rich feldspar, apatite, ulvöspinel, ferroan sahamalite, and secondary barite, and calcite.
Occurrence
Dorrite can be found in mineral reactions that relate dorrite + magnetite + clinopyroxene, rhönite + magnetite + olivine + clinopyroxene, and aenigmatite + pyroxene + olivine assemblages in nature. These assemblages favor low pressures and high temperatures. Dorrite is stable in strongly oxidizing, high-temperature, low-pressure environments. It occurs in paralava, pyrometamorphic melt rock, formed from the burning of coal beds.
Crystallography
Researchers conclusively determined that dorrite is triclinic-pseudomonoclinic and twinned by a twofold rotation about the pseudomonoclinic b axis. The parameters for dorrite are a=10.505, b=10.897, c=9.019 Å, α=106.26°, β=95.16°, γ=124.75°.
Chemical Composition
Calcium 8.97% Magnesium 5.44% Aluminum 6.04% Iron 37.48% Silicon 6.28% Oxygen 35.79%
Oxides
CaO 12.55% MgO 9.02% Al 2 O 3 11.41% Fe 2 O 3 53.59% SiO 2 13.44%
References
Text derived from https://en.wikipedia.org/w/index.php?oldid=1269655815 under CC BY-SA 4.0; modifications have been made.