Geo-pic of the week: Igneous Dike

igneous dike


100 million years ago, during the Late Cretaceous Period, a preponderance of igneous activity occurred in the continental region now known as Arkansas.  In fact, all of the igneous rocks discovered in the state were emplaced around that time.  Some of them are well known, such as Magnet Cove, located east of Hot Springs, or the diamond-bearing intrusion near Murfreesboro.    There are also lots of smaller igneous intrusions like the one shown in the picture above. 

Small igneous intrusions are found throughout the Ouachita Mountains.  There are so many small intrusions that new ones are regularly discovered.  Weathering at the earth’s surface has typically destroyed the original rock’s characteristics and what remains is mostly soft clay because the minerals that make up the intrusion are unstable under surface conditions. 

If you happen to notice an unusual-looking body of rock that cuts across the strata of a road cut or other rock outcrop when you’re exploring the Ouachita Mountains, it’s likely that you have seen a Cretaceous igneous dike.

5 thoughts on “Geo-pic of the week: Igneous Dike

  1. Samuel Walker

    Where is the exact location of this igneous intrusion? I am studying geochronology and tectonics of this region and am planning to visit some of these outcrops!

    1. argeology Post author

      This particular igneous dike is located in the middle of Lake Ouachita, so somewhat difficult to access. It’s on the south side of a small, crescent-shaped island at 34° 36′ 4.04″; -93° 17′ 4.69″. You may contact Richard Hutto at the Survey if you need additional locations for your project: 501-683-0151.

      1. Samuel Walker

        Thank you very much for this information! I will definitely be in contact with Mr. Hutto about additional locations to help me with my thesis.

  2. Ronald Barren

    I live in a North Central Arkansas very close to where silver was said to have been found. I know that most of these legends are just tall tales, but recently, I have found some rocks (indicator minerals) that have me a little more convinced that the stories may be true. If I can find a way to upload pictures, I will. Thanks! Ron B

    1. argeology Post author

      That is interesting. Galena and Sphalerite (ores of lead and zinc) have historically been mined in north central Arkansas, but not silver. If it would be more convenient, you can email your photos to me at and I’ll try to identify what you’ve found.


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