After an update to 6.10.21 I noticed that crushed ore sprites are not transparent. The other sprites are fine.
Thanks for the Report even if I already found that out yesterday right after the Release. Minecraft seems to have Issues with Grayscale PNG Files (after I ran all PNG Files through an Optimizer).
All Image Editors, Image Viewers and Browsers can see the Transparency just fine, but Minecraft says NOPE.