I always love this illustration. It has so much information to it. I
didn't know where I could find it again but Dana has used it for her
Accretionary Wedge 43 and now I'm copying it here here so I can have a reference to it.
They can also be hilarious. Observe:
Note
the upper left. One of my geo friends on Twitter posted this ages ago
(I wish I remembered who), and it still makes me giggle.
Thanks Dana for sharing and using this.
3-1-12 I also came across this QAPF on igneous rocks @ Sandatlas and have found this very helpful too.
Here it is, the classification diagram used for plutonic rocks:
QAPF diagram for plutonic rocks. The diagram was created by the
Subcommission of the Systematics of Igneous Rocks in the latter part of
the 20th century.
old
Few explaining words how to read
this diagram. There are four minerals or mineral groups chosen as
important cornerstones of the classification. These are quartz (Q),
alkali feldspars (A), plagioclase feldspars (P), and feldspathoids (F).
F and Q for chemical reasons can not exist together in one plutonic
rock. Other minerals may and almost certainly occur in these rocks as
well but they have no significance in this classification scheme. So,
the whole diagram is actually composed of two ternary plots (QAP and
FAP). To use the classification, the concentration (the mode) of these
minerals must be known and recalculated to make their sum 100%.
Example:
a plutonic rock that contains no alkali feldspar and no feldspathoids
but contains lots of pyroxenes (neglected in this diagram), plagioclase
feldspar and few quartz grains is probably gabbro
(located at the right edge of the diagram, little bit up from P
towards Q). The diagram doesn’t say whether it is gabbro, diorite, or
anorthosite. There are another criteria used to decide that. Note that
this diagram is not used for all plutonic rocks. Ultramafic rocks are
the most important plutonics that have separate classification diagrams.
Here's the QAPF_diagram link to it at Wikipedia
http://en.wikipedia.org/wiki/QAPF_diagram
I did have this at a different location since this is more appropriate for it I've moved it here.
No comments:
Post a Comment