White Chibia Granite

Macroscopic Description

Light-gray leucocratic rock containing scattered greenish gray nodules and silver platelets. The granular, phaneritic texture of fine to medium grain stands out. Constituent minerals generally have anhedric to subedric grains without lineations, cracks, pores or cavities. The rock shows no orientation, foliation, schist or apparent tectonic deformation.

Microscopic Description

CHARACTERISTICS

This is an acid rock of intrusive (plutonic) igneous origin, from the group of granitoids, composed mainly of non-dimensional quartz grains, feldspars and micas.

TEXTURE

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

MAIN MINERALS

Quartz (25%) that occurs in anhedric to subredic crystals. Alkaline feldspar (40%), occurring with anhedric to subhedric habit. Plagioclase (20%) in crystals with subedric or subidiomorphic prismatic habit. Some feldspars are zoned, and hydrolysis phenomena are observed, which promote their alteration. Biotitis (10%) that is chloritized, with subhedric habit and some prismatic minerals.

MINORITY MINERALS AND ACCESSORIES

Opaque (<1%) disseminated by sample mass, zircon (<1%) generally included in biotite.

SECONDARY MINERALS

Chlorite (3%) originated from biotite alteration processes. Clay minerals (3%) that occur in the nucleus of alkaline feldspars and altered plagioclases.

Technical Characteristics