Lichen - resembling old orange peel

[Bruce Williams]

Stony Stratford, Bucks. On old sandstone block.

Size: see scale bars.

Help with identification appreciated as always:



Bruce

[AlanS]

I think this must be Protoblastenia rupestris, despite the habitat.

P. rupestris is a lime indicator, occurring on limestone, on mortar and on concrete.
Some sandstones do contain appreciable quantities of lime (calcium carbonate) in the matrix that sticks the sand grains together, but could there be drainage from mortar? Or is this definitely sandstone that the lichen is on? (Church walls, for example, often have limestone blocks for decoration even if much of the wall is sandstone.)

Alan S.

[Bruce Williams]

I've just got back from a week's holiday so my apology for the late responses to your postings. Anyway, thanks for all your help Alan - it's good to have you back .

This lichen is on a large stone block (approx. 30" square by about 40" high) that originally supported a bronze plaque (long since nicked). It's literally covered with lichen of several different species and I'd just assumed it was sandstone because of its coarse texture. I think it's sandy and quartz-like rather than calcite but I will check it again when I next visit.

Bruce

[Bruce Williams]

Alan, I had a close look at the stone block today. As I mentioned before it is almost entirely covered with various lichens, however I found a clear area near the bottom that I could try scratching with a 50p piece. It scratched fairly easily producing a fine powder with no obvious quartz particles, so I guess it is probably limestone after all. The apparent coarse surface texture is probably the result of pitting due to weathering and old lichen growth.

Bruce