Strange Rock

[nimmers]

Can anyone identify this rock. My new home was built on old farmland.

 

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[Rookster]

You're right. It is strange.

 

[Geochem]

From only the picture I will try.

It appears to be "microcrystalline quartz". It is often a precipitation of silica from groundwater that occurs with limestone lithologies as a sedimentary process (non-metamorphic). They are often formed as "nodules", independent masses like your specimen.

The light blueish-green color sections in your rock are present due to elemental impurities present as the microcrystalline quartz crystals formed.

There also appears to be a shine or luster of the blueish-green color sections. This would indicate water molecules were also integrated in the silica dioxide process, giving the microcrystalline quartz have an opal mineral character. It takes a few percent water in the composition to be classified as an opal.

I would call your rock a high luster opaque to translucent tan to blue-green chert (or flint). Chert and flint are generalistic terms that can mean different rocks in different geographical locations. Microcrystalline quarts is a better term in focusing on origin, composition, and crystalline structure.

With other samples you have on your property, wearing safety glasses, break open one or so with a hammer. You should see "conchoidal fracture planes" - like arrowhead flint rock and glass. A rippled convex curved fracture with fairly sharp to touch edges.