Mineral facies are natural 'equivalence
classes' that partition the
p,T-environment (when they work
properly). Nevertheless, petrologists
have combined many; consequently, only
several cover the p,T-graph, to which
names have been assigned. These fields
and names have expanded and shrunk with
There has been a current suggestion to
eliminate the names of contact facies,
and some have been dropped by the SCMR.
How would this change our nomenclature?
In 1920, Eskola had not yet studied the
granulites of Lappland. Instead, his
facies changed with (comparable)
densities in the order: amphibolite
facies, hornfels facies, eclogite
facies. Recently, the amphibolite facies
absorbed the hornblende hornfels facies,
and the union was given the name which
had priority, 'amphibolite facies'.
If the granulite facies should absorb
the (pyroxene) hornfels facies, as has
been suggested, the union should be
given the name which has historical
priority, 'hornfels facies'. The SCMR
has been requesting suggestions and
Ce qui est simple est toujours faux, ce
qui ne l'est pas est inutilisable.