Quintinite is a

carbonate mineral Carbonate minerals are those minerals containing the carbonate ion, . Carbonate divisions Anhydrous carbonates *Calcite group: trigonal ** Calcite CaCO3 ** Gaspéite (Ni,Mg,Fe2+)CO3 ** Magnesite MgCO3 **Otavite CdCO3 ** Rhodochrosite MnCO3 ...

with the chemical formula Mg₄Al₂(OH)₁₂CO₃⋅3H₂O. The mineral was named after Quintin Wight of Ottawa, Ontario, Canada (b. 1935), who was a significant contributor to mineral studies at

Mont Saint-Hilaire Mont Saint-Hilaire (English: Mount Saint-Hilaire; abe, Wigwômadenizibo; see for other names) is an isolated hill, high, in the Montérégie region of southern Quebec. It is about thirty kilometres east of Montreal, and immediately east of the ...

. Quintinite is found as 2H and 3T, or 2-hexagonal and 3-trigonal, polytypes, which were originally approved as separate species, but have not been considered species since 1998.Bernard, J.H. and Hyrsl, J. (2004) Minerals and their Localities, 807 p. Granit, s.r.o., Prague (Quintinite, p. 503). These hexagonal and trigonal forms of quintinite are both from the hexagonal crystal systems, meaning they both have similar lengths of their crystal axes and the same angles between these axes. As a hexagonal mineral, quintinite has three axes of equal length at 60 degree angles to one another and a c axis perpendicular to these three axes of a different length. 2H occurs in

carbonatite Carbonatite () is a type of intrusive or extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geochemical verification. Carbonati ...

at Jacupiranga,

São Paulo São Paulo (, ; Portuguese for ' Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaW ...

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, in the Jacupiranga mine and 3T occurs with minerals like gonnardite and donnayite. Both polytypes occur in

hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspo ...

s in alkaline rocks. Herg (1977) interpreted the Jacupiranga area as related to a hotspot. The 3T polytype was originally found in the Poudrette quarry at

, which is a rare alkaline intrusive complex.Haring, Monik
Characterization and crystal-structure determination of UK 117 and UK 120, two potentially new minerals from Mont Saint-Hilaire, Québec
B.Sc. Thesis, Laurentian University, 2010 The 2H polytype is pleochroic, meaning that the mineral changes colors (in this case yellow and light yellow) when viewed at different angles under a polarizing petrographic microscope. The 3T polytype, however, is not commonly pleochroic but can show green pleochroism if it is high in iron. The 3T polytype has a positive index of refraction whereas the 2H polytype can possess crystals with either a positive or a negative index of refraction.

References

{{Reflist, 2 Aluminium minerals Carbonate minerals Magnesium minerals Hexagonal minerals Minerals in space group 182