LESSONS I LEARNED CABBING PREHNITE

*Don't Miss My Big Announcement at the End of this Blog!*

It was a bright, sunny day in Quartzsite, AZ when I saw a tarp on the ground with creamy light green stones, and I was smitten. It came all the way to Arizona from South Africa, just for me. The vendor only had rough and a few cabs (I don't remember seeing any slices), so I didn't see below the exterior bumps like the ones in this picture of the outside. 

Prehnite rough

 PROBLEMS AS A CABBING MATERIAL

Backlighting shows the structure inside the stone

First, the prehnite felt fairly soft to me when I was working it. According to Mindat.org, it's 6-6.5 on the mohs scale. When I was working on it, that felt like it was softer, but it took steel to scratch it, so I guess Mindat's  right. It is usually seen in translucent colors ranging from clear to green or yellow, or gray. One deposit of orange prehnite was discovered in South Africa.

The structural material visible in the back lit picture of a cab, was somewhat harder than the areas without it.  Also the black tourmaline inclusions have a mohs rating of 7, providing even more variation in the hardness when I'm shaping and polishing the stone.It doesn't seem like much of a difference when you look at the numbers, but it was really noticeable when I was working it. So as I tried to polish my first cab, I kept using very fine grits on it and the soft material ground out faster than the structural stone and tourmaline, giving me a bunch of low points, which, of course, wouldn't make a smooth surface.

YOUR LAPIDARY WHISPERER LEARNS

The next time I worked with this, I decided to go with a free-form shape and the prehnite cooperated a bit more (or maybe I was listening better). I also skipped my first wheel and went right to the 220 to start. I worked quickly and with a light touch. This time, I had a much better result as you can see in the picture at the top of this blog. Because of the nature of this material, I didn't really get a polish, but I finally did achieve a nice luster by not overworking the cab.

I'm glad I didn't get a lot of this material. I have one more smallish slab left, but I think it's going to spend some time in the box until it feels chatty.

Drop me a note and show me what you're up to in your lapidary shop!


ANNOUNCEMENT * DON'T MISS MY ARTICLE, "HARD ROCK MEALS" in the June edition of ROCK & GEM MAGAZINE! In it, I show how I created a case for shows that has a whole "meal" that's made completely out of rocks!!!

Come back on June 7, when I'm getting back inside rocks again. This time, it's not geodes, it's Thundereggs. Normally, they're not a favorite of mine, but wait until you see the cabs I've been able to make with what I've found inside!



See you next time,

Donna Albrecht
Lapidary Whisperer