Ap-1 Aplite

This rock exhibits two types of magmatic bands: one type has a milky white aspect, that under the microscope appears to be made of a very-fine aggregate of alkali-feldspar and quartz crystals; the other type shows a milky white aspect spotted with extremely small dark grey grains, that under the microscope are identified as tourmaline crystals. Tourmaline grains are also concentrated in centimetric dark grey orbicular structures, evident at the hand specimen. The rock sample comes from the Capo Bianco aplite (8.4 Ma), that outcrops in the marine cliff west of Portoferraio (Elba island) and that predates the Mt Capanne intrusion (see Elba granodiorite) (Geol.F.Trips, Vol.5 No.2.1 (2013), DOI 10.3301/GFT.2013.03).

Etymology: the term aplite derives from the Greek “haploos” (simple).

Thin section description: 

The field of view is largely occupied by a fine-grained matrix composed of alkali-feldspar (Afs), quartz (Qz) and tourmaline (Tur) crystals. These crystals can be identified in the PPL view since Qz crystals are clear, Afs crystals show a slight clouding and Tur crystals exhibit the distinctive strong olive-blue pleochroic colours.

Thin section PPL	Thin section XPL