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Tuesday, November 8, 2016

Identify this Fossil?

Some of the floors and the walls of one bathroom at Fourmilab are tiled with Jura beige limestone. This is a natural stone, typically with a beige/tan/light yellow colour, available in a variety of finishes, from rough to polished. The stone at Fourmilab is of the rough variety. The stone has texture and colour that varies within tiles and from tile to tile: if you're looking for consistency, look elsewhere. There are all kinds of details in the stone, including pseudofossils such as dendritic fractal mineral inclusions like the one below.


While this looks like a fern or similar plant, it is created purely by a diffusion of a darker material into the limestone.

A couple of days ago, I happened to notice the structure below when it was illuminated by oblique sunlight. The tile has been in place for 25 years, but I'd never seen it with favourable lighting that made the feature apparent. While the inclusion above is purely an albedo (light and dark) feature, that below is raised above the surface of the tile and best seen with light incident at a low angle.


The picture was lit by a LED flashlight held near the tile at the left to highlight the relief. The bluish light of the flashlight washed out the normal yellowish colour of the tile. The centre looks darker in this picture due to shadows cast by the oblique light. The photo below shows a detail of the centre with direct light and natural colour. It looks like there may be some kind of structure in the “stem”, but I can't make sense of it.


To my eyes, this looks more like a plant than something formed through mineral processes. Is it indeed a fossil? If so, can anybody identify it? Please use “Send Feedback” to reply with any clues.

Thanks in advance!

Update: It's a fossil of Saccocoma, an extinct free-floating crinoid from the Jurassic period. Thanks to Mike Huggins who identified the fossil! (2016-11-08 01:36 UTC)

Posted at November 8, 2016 00:06