The following samples were in strata contemporary with large animals.

1) The specimen must be captivated in an oxygen-deficient environment, like rapid burial under large layers of sediment, to prevent decomposition for a sufficient duration to permit mineralization and an exchange of organic material for mineral.

2) There must be present soluble minerals like silicates, aluminum, oxides of iron, etc. to penetrate the specimen.

Much like a photographic negatives with different densities of gel and immersed in developing solution displaying visible contrast of the gel density, likewise, minerals will absorb in different quantities according to porosity, stratification, and density of the biological specimen. 

Where a plant is grown in a consistent environment with stable temperatures and moisture, no growth rings are formed; thus, there are no denser portions to accept different quantities of minerals and NO VISIBLE GROWTH RINGS. No such conditions exist on earth today and growth rings are formed in the tropics; however, petrified palm trees have no growth rings but look like a mineralized honey comb.

These processes are no mystery to a Christian or scientist who believes in a perfect environment before the flood, and who believe the Lord will not take millions of years to evolve another Earth, as the LORD promises in Isaiah 65:17: