"Basalt Eggs"-Millington, New Jersey

Hi all; Next to the Millington Quarry in Bernards Township, NJ, construction of a subdivision is underway. There is some kind of retention basin there and while I was having a look around, I found many of these "Basalt eggs" as I like to call them. These things were everywhere and I was curious what they really are-that is, do they have a proper name? Many thanks.

David,

These look like concretions. Were they found in or adjacent to the Sandstone? Are there any traces of zeolites in the "eggs" or other minerals?

Best,

Joe

Hi Joe; Not one Zeolite to be found. To be honest, I can't remember if there was any Sandstone nearby. Maybe I'll take a run over today and look again. About ten minutes from my house.

Hello,

It looks like basalt spheroidal disjunction.

best regards,

Ricardo

From the photo (which is a bit blurry), they look more like iron concretions than basalt. Definitely check to see if there are sandstones nearby, as that could be your source......

Hi Paul; Thanks for the post. The material is not magnetic so I don't think it is Iron. I did go back to the site yesterday only to find that the who basin had been filled in. But I did find another subdivision with similar material and lots of Sandstone. I take it that is significant for some reason?

An added bonus to my quick trip was finding a very nice chunk of Amethyst lying amidst the rubble of what will most likely become the foundation of yet, another expensive home.

"The material is not magnetic so I don't think it is Iron. "
Iron concretions do not consist of (native) iron; they are built of limonite which is non-magnetic.

Hi David,
Ricardo is correct! I live about 2 miles north of the Millington Quarry and over many years I have found this spheroidal disjunction of basalt as a very common happening aound surface exposures of basalt. Very rarely do you see any interesting minerals but they are often stained or coated in iron rich compounds like geothite etc. Over the centuries many houses and rock walls have used this material. Handy field-stone construction of the foundations used this free local material in 18th and 19th century periods. Keep an eye out for this as you drive around the local townships.
Steve.