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(DSM #SD13) Septarian concretions form in cavities where the outer rock is cracked and angular. Minerals fill the cracks and preserve their shape.

(DSM #SD11 and #SD12) Concretions come in all sizes and are very often mistaken for fossils because of their intricate and strange shapes. They form when a grain of sediment or organism acts as a nucleus for minerals to precipitate and grow. Some…

(DSM #SD8) Geodes are crystals that form to fill a void. The outer portion of the stone is usually non-descript and plain but the crystals show themselves when the rock is hit with a hammer.

(DSM #SD7) Dendrites are iron or manganese oxide mineral growths that occur in a rock after deposition.

(DSM #M76 and #M172) These interal casts show the shape of the inside of a cavity such as a shell or brain. When you have an imprint of the outside of an organism it is calleda mold.

(unnumbered) Compression fossils most often form in sedimentary rocks called shales which form in the bottom of lake or sea beds. The same fossil can be seen in both the part and counterpart but different features are often preserved on both sides.…

(DSM #PL58) This section of palm wood very clearly shows how individual cells of an organism can be filled with minerals in the process of permineralization.

(unnumbered) Petrified wood often exhibits a combination of replacement and permineralization. This specimen clearly shows how the cell walls have been replaced with minerals. The cells themselves are also filled in some cases.