Strange potato rock with crystal inclusions

[Darklingchild]

https://www.instagram.com/p/ByW77vHAoq4/?igshid=1avo7yml7tj9sI found a strange rock the size and shape and color of a potato. But it has strange cracks crisscrossing the surface they are Crystal's of some sort and harder and quartz. While the rest seems to be comprised of some sort of sedimentary rock. 

[d_day]

That is a septarian nodule that has partly eroded. It’s a type of concretion. They start off as a ball of mud, and dry out, which leads to internal cavities called septs. As water brings minerals inside, (usually calcium carbonate) they form crystals (typically aragonite and/or calcite) inside. They are quite stunning when cut an polished. 

Also, the mud balls usually form around something, called a nucleus. Sometimes it’s just a grain of sand, and sometimes it’s an interesting fossil. They can be found all over the world.

[23XLive]

If you decide to cut it, I would love to see pictures of what the core looks like!