Cummingtonite

Description

Cummingtonite has a hardness of 5 – 6 and a specific gravity of 3.1 – 3.6. Originally named in 1824 by Chester Dewey for the type locality in Cummington, Massachusetts.

Found in around 350 localities worldwide and 16 within Colorado, Cummingtonite often occurs “in medium-grade regionally metamorphosed rocks; characteristic of metamorphosed iron formations; also as a late-stage mineral in some gabbros and norites; rarely in silicic volcanic rocks” according to Mindat, commonly associated with Rhodonite, Chlorite Group and Garnet Group minerals, Corkite, Magnetite, Talc, Spessartine, Fluorophlogopite, Arsenopyrite, and Clino-ferro-suenoite.

WebMineral analyzed a specimen and found it to contain roughly 49% Oxygen, 29% Silicon, 22% Magnesium, and a trace of Hydrogen. Especially in comparison to Magnetite, this would make for a great representation of Magnesium and how it can look so differently at times! But, it might be a little too big to fit into any periodic table, so consider bringing this home only if you have a larger display cabinet!

There’s nothing really inherently incredibly valuable with this mineral as it’s not usually mined for its Magnesium, but it’s a cool rock still and a pretty rare mineral, and at least you’ll now know what you’re looking at if you find a rock like this on your next hike