Unknown Lycopsid - crenulations and erosion of exterior?

[Kato]

Wandering about I found some slivers of porcelain like permineralized material floating on the surface in a small dry wash.

 

 

Exposed and opened a small trench of very broken up pieces of a Lycopsid. I'm going to very tentatively guess Sigillaria due to presence of crenulations on the remaining margin of the material. Covered the pocket back up after taking a few photos. The overall pocket length was at 3 feet when I quit. Specimen increasing in size and going deeper into the hill than my little digging knife could handle. Nearby plant roots had entered the specimen and succeeded in breaking it up into chunks.

 

In this photo one can see areas of black, red and pink surrounding the exposed permineralized specimens.

 

Learning questions:

 

(1) I'm going to guess this is degradation of the former exterior?

 

(2) Colors suggest iron content and/or maybe some carbonization?

 

(3) Are there some papers whereby I can learn more characteristics to help narrow down otherwise hard to ID Lycopsids?