A marble-sized chunk was put through 10 freeze/thaw cycles to create a fine sludge. I then examined a few drops of the diluted sludge under the scope to get a preview of what was in there. It was immediately obvious the sample was overwhelmingly dominated by a small centric species - possibly Cyclotella (but I'm not sure). However, a (very) sparse smattering of other species warranted moving on to a full clean to see what else could be found.
After the usual acid treatments, rinses and silt separation stages, I ran the cleaned sample through a fine mesh that let material of 30um or less pass through and held back anything >30um. The fine material (mostly cyclotella) covered the bottom of a 250ml beaker in a 1mm thick layer but there was only enough larger material to make a single strew!
As discovered from examining the sludge, the fine material was pretty much all Cyclotella (?) but with other species sparsely dotted around.
The coarser stuff proved to be nearly all (freshwater) diatoms too, though most were pretty battered. I was able to pick out a few good 'uns though, enough for a small quick and dirty mount. Strangely, I found no sign of two of the species photographed when previewing the uncleaned sludge!? They must be very rare in the sample, but there are probably more in the unprocessed rock.
So no vast array of exciting species; I could find most, if not all of them in the local pond. But an interesting diversion all the same.
