the bedrock
basalt
trap rock · incl. amygdaloidal
The tell
Heavy for its size, evenly dark grey-black all the way through, and no layering at all. Shale splits into sheets; slag has bubbles and usually a colour in it when you hold it to the light.
Amygdaloidal basalt, the kind with gas pockets filled by later minerals, is the parent rock of half the Keweenaw list. Datolite, thomsonite, greenstone and agate all grew in holes in basalt.
What it gets mistaken for
- black shale
- leland blue
- frankfort green
- slag
- dark limestone
The facts
- also calledtrap rock · incl. amygdaloidal
- age~1.1 billion yrs
- where it turns upevery shore · glacial float
- on the chartthe bedrock · 1000 stickers ever
Put it on the shelf
Every stone on this chart is drawn and kiss-cut at three inches. The rarer the stone, the fewer exist: only 1000 basalt will ever be printed, then the run is retired.
10% of every order goes to the Roscommon County Animal Shelter.