Volcanic heavy deep purple (red/violet?) or red(?)

[watershield]

neat what you can find if you look.
Those holes are the result of hot lava being cooled quickly in water,
At one time a good portion of the western US was covered by an inland sea, (the Albian Sea) Shifting land masses, mountain building, etc, pushed that sea North into Northern Alberta Canada.
The wight of that water moving north also pushed various oil pockets north as well, creating the Fort McMurray Oil Sands.

[Jen]

Awesome gifts of nature.

[watershield]

I would love to see that old glass you mentioned. I collect glass and have a fair library on the subject.
Primary collection of Cruets (oil & vinegar bottles). Over 150 items last count.

[watershield]

Greentown Glass....almost forgot about them. I've got a few toothpick holders made by them. Holly pattern for sure, in an amber slag glass.

Back to your rocks.....
When we look at old worship sites from around the world, I mean really look. The materials used, the way they have been placed, etc it's not hard to see that the old races new a lot more about the science of worship then one might think.
Stonehenge is a good example. For a long time it was thought it was just an elaborate calender. Now they know it's also a very effective amphitheater. Interestingly however, while the voice resonates within the stones, it's not audible outside the stones.
Now hows that for technology