zeolite – Georneys

amygdaloidal basalt — Amygdaloidal basalt collected during dredging along the Ninetyeast Ridge in the Indian Ocean in summer 2007.

def. Amygdale (also spelled Amygule):
Vesicles, generally in extrusive igneous rocks, that are filled with secondary minerals, most commonly quartz, calcite, chlorite, and zeolite.

When a rock contains amygdales, geologists often describe it as an amygdaloidal rock. For example, basalt is often described as amygdaloidal basalt.

Here are a few previous, related geology words of the week that may be of interest:

V is for Vesicle (and Vug)

Z is for Zeolite

M is for Magma

And here are a couple more pictures of amygdaloidal rocks:

amygdaloidal basalt2 — Amygdaloidal basalt from the Isle of Skye, Scotland. Picture courtesy of Matt Kuchtam.

DSC06418 (1) — A zeolite amygdale in a rock collected from Quartzville, Oregon. Picture courtesy of Dana Hunter.

***Thanks to my twitter follower Laura Hamilton for suggesting this week’s word. Thanks to Matt Kuchtam, Dana Hunter, and Lockwood De Witt for providing pictures.***

Natrolite, a mineral belonging to the zeolite group. Mary's Peak, Oregon. Picture courtesy of Dana Hunter.

def. zeolite:
The name of a large group of porous, framework, aluminosilicate (their basic structure is interlocking tetrahedra of SiO4 and AlO4) minerals that contain significant water and also significant exchangeable cations, which makes them absorbent materials. The name zeolite originates from the Greek words “zeo”, which means “to boil”, and “lithos”, which means “stone”. Zeolites were given their name because when you heat them, they generally release water in the form of steam. There are dozens of minerals in the zeolite group. You can view a list of zeolite minerals here. Zeolites often form through the interaction of volcanic rocks and ash with alkaline groundwater. Thus, you can often find spectacular and very beautiful zeolite crystals inside vesicles and vugs (often creating amygdules or crystal-filled cavities) in volcanic rocks such as basalt. Zeolites also crystallize in shallow marine basins.

My good friend and fellow geoblogger Dana Hunter has provided me with zeolite pictures galore. She took these pictures during one of her geology trips with Lockwood DeWitt. Thanks for the pictures, Dana and Lockwood!