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Each of these minerals has a different initial rubidium/strontium ratio dependent on their potassium content, the concentration of Rb and K in the melt and the temperature at which the minerals formed.
A Rb-Sr date which is at variance with other geochronometers may not be useless, it may be providing data on an event which is not representing the age of formation of the rock.
There are considerable differences among varieties, and some are mutually unintelligible. "Legislating diversity in twenty-first century Mexico".
Huasteca Nahuatl, with over one million speakers, is the most-spoken variety. de enero de 1547, 2 vols (Facsimile edition of original MS.). "An Image Is Worth a Thousand Words: Teotihuacan and the Meanings of Style in Classic Mesoamerica". Latin American horizons: a symposium at Dumbarton Oaks, 11th and 12th October 1986.
The ideal scenario according to Bowen's reaction series would see a granite melt begin crystallizing a cumulate assemblage of plagioclase and hornblende (i.e.; tonalite or diorite), which is low in K (and hence Rb) but high in Sr (as this substitutes for Ca), which proportionally enriches the melt in K and Rb.
This then causes orthoclase and biotite, both K rich minerals into which Rb can substitute, to precipitate.