Sometimes I find wonderful Prehnite on the mine dumps in the Keweenaw Peninsula.
If prehnite forms in veins, as it does in the Keweenaw Peninsula, it generally associates itself with native copper. I love to find these rare pieces that make lovely jewelry, with the apple green of the prehnite surrounding the shiny copper.
Most of the Prehnite of the Keweenaw is vein Prehnite. In vein Prehnite one cannot notice the chatoyant needle-like crystal structure normally associated with larger non-vein Prehnite pieces such as the gemmy pieces found in Australia and other locals around the world. Feather-like Prehnite crystals are seen in U. P. Thomsonite which is actually variegated and non-variegated Prehnite. Pink, red, and green, and other color combinations can be found, depending on what minerals flowed into the vesicles and veins along with the Prehnite. Locals refer to pastel Prehnite permeated with copper flecks found on the beaches in the Calumet, and also in the Copper Harbor area as “Patricianite”. These Prehnite pebbles can be jewelry grade, and are wonderful to collect as they roll in with the Lake Superior breakers.
Prehnite is very solid, but brittle, so care must be taken when cutting it. Stay away from new grinding wheels and rough grits. Harmonic vibrations can blow apart this material.
High quality Prehnite is available from various locations throughout the world, but when you add the native copper to the Prehnite from the U.P., you can’t beat ours.