Wonder if these are pseudomorphs after a more likely metamorphic phase, in fact, a member of the actinolite/ tremolite series, as you initially thought. Asbestiform and plumose morphologies of this series can be replaced quite nicely by a carbonate material.
There's an interesting possibility. It wouldn't be too challenging to get the chemistry, if there was any skarn formation. In other places, a few miles from this location, sills in the carbonates definitely DO make skarns locally, although mostly epidote as the evident calc-silicate, at hand-sample scales. There are plenty of possible conduits for hydrothermal activity even away from the local intrusion - faults, abundant fold-related cleavage in the massive carbonates, etc. - so later replacement by calcite would not be difficult. Thanks for that suggestion!
Interesting estimation of what happened, Richard, no silica, so it's not wollastonite, apparently? --I purchased a couple of white Ca-silicates cheap, then went to study them and found out what a rabbit hole those are! You've heard of black uglies, these are white uglies....but Jox Rox on the far NE side of Indianapolis sometimes has odd minerals available. But he doesn't mail stuff. I used to pass through there occasionally.
Wonder if these are pseudomorphs after a more likely metamorphic phase, in fact, a member of the actinolite/ tremolite series, as you initially thought. Asbestiform and plumose morphologies of this series can be replaced quite nicely by a carbonate material.
There's an interesting possibility. It wouldn't be too challenging to get the chemistry, if there was any skarn formation. In other places, a few miles from this location, sills in the carbonates definitely DO make skarns locally, although mostly epidote as the evident calc-silicate, at hand-sample scales. There are plenty of possible conduits for hydrothermal activity even away from the local intrusion - faults, abundant fold-related cleavage in the massive carbonates, etc. - so later replacement by calcite would not be difficult. Thanks for that suggestion!
Interesting estimation of what happened, Richard, no silica, so it's not wollastonite, apparently? --I purchased a couple of white Ca-silicates cheap, then went to study them and found out what a rabbit hole those are! You've heard of black uglies, these are white uglies....but Jox Rox on the far NE side of Indianapolis sometimes has odd minerals available. But he doesn't mail stuff. I used to pass through there occasionally.
It effervesces even microscopically with the tiniest drop on very local parts of the plumose material, so I'm pretty sure it's virtually all calcite.