Black on Fossil

[jeannie55]

Recently, I hunted along the banks of the Grand River. I found many fossils in gravel and since my husband is complaining about my rocks and fossils taking over the house, gravel is good. The soil was black but it did t look like it was oil. I’ve volunteered a couple of time at oil slicks, cleaning the beach, bathing birds and very cute little seals. We went back every year for a while and the oil stained but was also slightly slick feeling. This dirt wasn’t slick and it didn’t transfer like oil does. But a few of the gravel are stained black. At first I thought it was a natural occurring pigment like we see around Magnet Cove in Arkansas. After a while o began to think it’s black from an oil spill that happened a few years back. The black cones off if I use a little force with the dental pick and it isn’t sticky or oily. My question is two fold: if the black is oil stains is it harmful to my pets or family and is there a chemical that stains rocks black? I know you cannot tell much by pictures but I am going to try and post one. Thanks for any insight or information any of you can provide. 

[Scylla]

Several minerals stain rock black such as manganese oxides. Yours might be algae or bacterial biofilm since it comes from a wet environment. If it is degraded oil, I would avoid eating it. If you clean the rocks with soap and water and don't let the pets or family members put the rocks in their mouths, you should be safe.

[jeannie55]

Thankfully all my grandchildren are beyond that oral stage where everything goes in the mouth. The dogs are another matter. I will be extra vigilant in keeping dogs out of rocks. Thank you so much for sharing your knowledge. 

[Scylla]

3 minutes ago, jeannie55 said:

Thankfully all my grandchildren are beyond that oral stage where everything goes in the mouth. The dogs are another matter. I will be extra vigilant in keeping dogs out of rocks. Thank you so much for sharing your knowledge. 

You are welcome!