x-ray diffraction crystal-structure analysis of omphacite from eclogite , tiburon peninsula , marin county , california , shows that this clinopyroxene has p2 symmetry with a nearly ordered distribution of the multiple cation content defined by its approximate formula : ( na ( o.5 ) ca ( o.5 ) ) ( mg ( o.4 ) fe ( 2 ) + ( 0.1 ) al ( 0.4 ) fe ( 3 ) + ( 0.1 ) ) si ( 2 ) 0 ( 6 ) .
C3829197
marin county
C0006754
california