Fossilized Egg?

[lomaalta]

While clearing rocks today, I found this one.

It LOOKS like an egg that fossilized then was later broken in half - exposing yellow (obviously fossilized) yolk. This is definitely the color of the rock, and not a stain or anything.

Could it be what it looks like?

In the depression there are what appear to be ribs or fingers, although you probably can't tell by this picture.

It's about 2 1/2 inches in diameter.

Thanks.

Edited November 13, 2013 by lomaalta

[Auspex]

What you see is the result of geological processes, not biological. It appears to be a quartzite cobble with a vug in it.

[lomaalta]

Thanks it's actually a flint nodule... there are gazillions here.... broken in half long ago - so the white surface (or the inside if you broke it again) would be chocolate brown - but sun exposure has whitened it... if that makes any difference. I have never found such a bright yellow anything here. Thanks.

[lomaalta]

Here is a better pic of it.

What mineral would that yellow be?

Edited November 13, 2013 by lomaalta

[painshill]

It does look like a chert nodule (although Americans would call it flint). The yellow material is likely chalcedony. If you can see any suggestion of a fibrous structure under a magnifying glass that's for sure what it is.

Incidentally, egg yolks are not always yellow. The yellow colour we are familiar with in poultry eggs is from fat-soluble carotenoids arising from a diet that includes plant material containing those pigments. Eggs from free range chickens fed on soya pellets may have yolks that are almost white and carotenes are added to the feed to "correct" that. The yolks of eggs in carnivorous and many omnivorous animals are generally not yellow. Organic pigments such as carotenoids wouldn't survive the fossilisation process while retaining their colour anyway.

Edited November 13, 2013 by painshill