Gabbro is the plutonic equivalent of the volcanic basalt. It is characterized by its gray, dark gray and black colors may have bluish or greenish tone. It has a granular texture and coarse-grained crystals. It measures 9.8 cm. in length, 7.35 cm. in width and 3.3. cm. in thickness.
Gabbro (probably from L. glaber, smooth) oftenly exhibits layering structure, defined by alternating layers of light and dark colored minerals. Individual layers vary from several meters to a centimeter or two in thickness and field observation indicates that layers are arranged like a stack of saucers. If the rock has been affected by earth movements such as folding or faulting, the layer may be steeply inclined. Gabbros are deposited as stocks, sills and dikes.
This igneous rock has an accession no. NMR-2930 is one of the several rocks which shows distinct mineral composition. It was collected in Matiko Creek Sapang Maasin Quezon, Palawan on November 4, 1997. Other localities are Bulacan, Antique, Iloilo, Aklan, Agusan del Norte, Marinduque, Zambales and Camarines Sur.