Olivine basalt with a vesicular structure

THANK YOU FOR YOUR ANSWER FENG. IT IS A POSSIBILITY. PLEASE NOTE THAT THE ROCK LACKS PLAGIOCLASE AND CONTAINS MELILITE (SEE NEW PHOTO ATTACHED). ALSO, THERE IS A QUARRY NEAR HEIDELBERG (ON KATZENBUCKEL) WHICH HAS NEPHELINITE AND I THINK THERE ARE ALSO OTHER ALKALINE VOLCANICS AROUND THE AREA.

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IOANNIS

There is only one response: try and make a thin section or have somebody conducted a quantitative XRD analysis. I know the Katzenbuckel and its petrology from browsing the literature. You are right on the alkaline track but for a more detailed answer you need more hard facts than the outward appearrance of a hand specimen

HGD

DEAR HARALD

THANK YOU FOR YOUR REPLY. I WAS JUST WONDERING WHAT THIS ROCK COULD BE BY EXAMINING IT IN THE OLD SIMPLE WAY, MACROSCOPICALLY.

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Dear Ioannis: if the rock is volcanic, lacks plagioclase and contains melilite, then it is not a basalt, but an olivine melilitite, a very undersaturated rocks, and surely might hold mantle nodules. But, a thin section petrography is mandatory. Regards, Sebastián.

DEAR SEBASTIAN

THANK YOU FOR YOUR REPLY. I AGREE THAT AT THE END A THIN SECTION IS NEEDED.

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IOANNIS

Previous answers refer to the mineralogical classification of the rock, but what type of rock is it? There are a lot of cavities, so it might be a scoriaceous lava or just a scoria. It looks like it is composed of many small fragments welded together.

THANK YOU FOR YOUR ANSWER BRIAN. I AGREE THAT THIS VOLCANIC ROCK IS SCORIACEOUS.

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IOANNIS