Black Jade Granite

Macroscopic Description

Melanocratic rock, dark gray in color, containing scattered black crystals of centimeter dimension. It stands out for its granular, phaneritic texture of fine to medium grain. The constituent minerals generally have grains with anhedric to subhedric shape and some with prismatic tendency, without lineations, cracks, pores or cavities. The rock shows no orientation, foliation, schist or apparent tectonic deformation.

Microscopic Description

CHARACTERISTICS

This is a basic rock of intrusive (plutonic) igneous origin, composed mainly of non-dimensional pyroxene and plagioclase grains.

TEXTURE

The rock has a holocrystalline, phaneritic, non-equigranular texture of medium to coarse grain, with a hypidiomorphic tendency.

MAIN MINERALS

Ortopiroxenas (40%), occurring with anhedric or prismatic habit. Clinopyroxenas (20%), occurring with anhedric to subhedric habit, sometimes presenting alteration halos. Plagioclase (35%) in crystals with subedric or subidiomorphic prismatic habit, with hydrolysis phenomena, which promote its alteration.

MINORITY AND ACCESSORY MINERALS

Olivine (3%) and opaque (<1%) disseminated by sample mass.

SECONDARY MINERALS

Clay minerals (3%) that occur in the nucleus of altered plagioclases and disseminated iron oxides.

Technical Characteristics