the GNU version of the Collaborative International Dictionary of English
adj. Pertaining to, or consisting of, feldspar.
The Century Dictionary and Cyclopedia
Pertaining to feldspar or containing it: an epithet applied to any mineral in which feldspar predominates. Also written felspathic.
Word Usage
"The rock here is a porphyritic granite (porhyritic meaning that the stone has large-grained crystals, such as feldspar or quartz, dispersed in a fine-grained feldspathic matrix or groundmass)."