Hello WWalt, thanks for the pictures!
I'm going to go with the Vesicular Basalt.
Here's a paragraph I found on the WikiLink for Basalt about the magnetism.

"The mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene. Olivine can also be a significant constituent.[46] Accessory minerals present in relatively minor amounts include iron oxides and iron-titanium oxides, such as magnetite, ulvöspinel, and ilmenite.[41] Because of the presence of such oxide minerals, basalt can acquire strong magnetic signatures as it cools, and paleomagnetic studies have made extensive use of basalt.[47] "