Obsidian, Shelf Specimen

Description

Obsidian shelf specimen from the Tarawera volcanic eruption of 1886 in the Bay of Plenty Region, New Zealand.

Formed during the eruption of Mt Tarawera near Rotorua in June 1886 at the margins of rhyolitic flows.  Contains pumice and perlite inclusions formed by contact with groundwater.

In the classroom, explore differences in structure compared to other rocks from felsic lava such as pumice or rhyolite.

Colour: black to black/green

Fracture: conchoidal

Mohs hardness :5-6

Specific gravity: ~2.4

Specimen is 16x8x6cm, weighs 1076g.

Photograph is representative only.