Formed about 70 million years ago, septarian nodules (also known as dragon eggs because they look like they have scales) occurred when volcanoes erupted and caused dead sea life to form mud balls in nearby sediment. As they shrank in size, cracks were created and sea shells found their way into the cracks, eventually creating calcite crystals. Then, through the magic of mother earth, the mud balls tended to crack at 7 points, creating the scaled pattern.
Septarian is a combination of aragonite (dark brown), calcite (yellow crystals), and limestone (tan outer material). Metaphysically, it has grounding earth energy, brings the feng shui element of wood, and it is a great stone to have around when you need some calming energy.
You may find the nodules intact and smooth, or they may be like the one pictured with part cracked open so you can see the inner crystal structure.