What have I discovered

[Gypsy89]

 

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[Terry Soloman]

That is genuine basalt! Congratulations, and welcome to the forum!

 

[A2coins]

Welcome from Mi. Tommy

 

[DetecTom]

Basalt is cool and looks like some kind of moon rock. Although, volcanic rock is cool in itself.

 

[dognose]

Nice looking Rock.

Tell us about how you found it please, in what context was it found?

The marine shells in it are a neat addition.

 

[ticndig]

thanks for the I.d Terry , got my learning in for the day . I make a point of learning something new every day , and it's easy enough to do on Treasurenet.

 

[EQ8]

Petrified sponge maybe?

 

[Red-Coat]

I don’t think that's basalt (or volcanic). I don't see any evidence of petrology consistent with igneous formation. The size and geometry of the holes are also not consistent with them being vesicles. I think that's a chunk of 'tufa', which is a type of highly porous limestone within which the cavities are formed by erosion and/or have arisen from the presence of gastropod and mollusc activity. It frequently contains residual shells and shell fragments.

Sedimentary tufa is frequently confused with the ‘similarly’ named ‘tuff’, which can have a similar superficial appearance and may also contain shell debris. Tuff has a volcanic origin but can in a sense also be regarded as sedimentary since it is often formed from compacted depositions of volcanic ash/ejecta. The petrology of tuff can also be basaltic (as opposed to rhyolitic, andesitic etc) but, if so, it’s usually a very dark rock: black, dark green or red and almost always contains visible phenocrysts or glassy inclusions.

Based on the nature of the cavities and the absence of any visible phenocrysts etc, I would go with tufa rather than tuff. An acid test would tell you for sure if the rock has a carbonate matrix rather than a silicate matrix but you would need to test a virgin surface. The cavities in weathered tuffs frequently have secondary deposits of other minerals such as calcite.

 

[claypile]

These are historically beautiful, these will never get out-fashioned.