July 15, 2019
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I bought the marble block below to use for practicing marble sculpting. The original source is unknown as I bought it from a place that had salvage marble.
The fellow who sold it to me said it looked like typical Colorado architectural/decoartive-quality marble. These blocks used to be part of some church steps somewhere in East St. Louis IL, many years ago.
From the outside this marble looked white with faint soft gray streaks in it, and the occasional brown crystal visible on the surface.
The image below shows some basic measurements.
The image below has more writing on it to explain the different features visible.
I cut this whole piece off of a larger piece. The marble saw I have can only cut about 2.5 inches deep, so for this block (9 inches thick) I had to make slices on both sides, and then split it the rest of the way using flat wedges. Areas #1 and #2 is the initial cut depths, and area #3 is the center section that was split (broken) apart during this step.
Then I drilled a series of five holes and used leaves and wedges to split it further. Note #4 is pointing to one of the wedge holes.
The reason to use leaves and wedges and not just saw it again was to avoid another sawn surface... I prefer my sculptures to have a more-natural looking surfaces if possible, and sawing a surface leaves it totally flat.
Item #5 is showing the holes where two smaller pieces broke off. I didn't expect I'd be using this stone for show & tell so I didn't save those little pieces, but that is the reason why those two big holes are visible there.
In this picture you can see the typical pattern in cut area #2, of the faint gray streaks.
In the #3 broken depth area, you can also see a lot of those little brown crystals. Near the top there is lots of little ones, and near the bottom there is a few bigger ones.
Below is a photo of the top part laid open in front of the bottom part. And it turned out that there is rather a lot of those crystals in there, some of them kinda big...
The brown crystals are probably axinite.
...In some parts of the world axinite crystals get big enough and pure enough to be semiprecious gemstones, but not wherever this marble came from it seems. These crystals look big but from the end they look like a very-narrow playing card "diamond" shape. You can see them well because you are seeing the broad sides of them.
In the upper-left area is a "U" shape in the rock where I tried to dig out a larger one. It didn't turn out to be really that large when I got it out. My carbide stone-cutting tools kinda battered it, and the ends of the axinite crystal were not real well defined, it just kinda faded into marble.
Below is a close-up of some of the larger crystals.
It is difficult to photograph but they do look nicer than the photos suggest.... -at certain moments.
They are light brown most of the time but shine bright yellow when the light catches them just right.
The green arrow in the image below is pointing to a crystal that is lighting up from the camera flash.
The presence of the brown crystals doesn't make the marble unusable for carving, as carbide can smash through it and diamond will grind through it--but it does mean that anything I made from it is likely to have some small brown spots in it. And might have a few big spots...
If you use salvage architectural stone for art carving, this is a common risk. Art stone would be selected to have as few impurities in it as possible, where with (decorative) architectural stone the standards are not quite so picky.
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