FMF - Friends of Minerals Forum, discussion and message board

[vdhinesh79]

I found this rock washed ashore along the marina beach chennai india. Want to know what type of rock it is ? It is black in color around the edges.

[Tobi]

It looks like a lava rock ...

[vdhinesh79]

When I was walking along the shores of the beach, I watched it being being washed ashore by the waves. It is rather heavy for its dimensions but there is no iron content in the rock. Is it normal for lava rocks to be found like this?

[James Catmur]

Pumice and similar volcanic rocks float on seawater. You can read more about it here:

https://www.mindat.org/min-48576.html

Could it be oil from an oil spill (try burning it to see)?

[SteveB]

A low density volcanic mineral similar to pumice if you break a piece off you should be able to see the inside colour and see if its uniform throughout or only dark near the surface where it may have absorbed marine pollution like waste oils that have combined with seas floor sludge. possibly broken loose from anchor damage. It doesn't show signs of rounding from being loose in the beach surf for long if it smells of oil it absorbed some pollution.