This is a high-pressure and high-temperature polymorph (version) of quartz.

This is also an important conclusion. The authors present evidence of that the variation in Sr-Pb-C is not a pure mantle source, but incorporates 'crustal signatures' from the melting of subducting slabs.

If a magma crystallizes stable plagioclase, most of the Eu will be incorporated into plagioclase, causing a higher than expected concentration of Eu in the mineral versus other REE in that mineral (a positive anomaly). This is because Eu's reduced divalent (2+) cations are similar in size and carry the same charge as Ca2+, an ion found in plagioclase so it can substitute easily in the plagioclase crystal lattice.

Canada (Baffin Island) is similar to Brazil in that the continents are made up of cratons. Cratons are old and stable parts of the Earth's crust. These cratons are commonly studied for clues into the Earth's early history.