Calcium oxalate is the most frequently found crystal in plants. Its crystals have been reported in more than 200 plant families. Calcium oxalate crystals observed in the Solanacea family form unique pseudotetrahedral and chiral morphology, although the molecular structure is achiral. Additionally, the crystals extracted from some plants of this family possess some extra faces. The present paper concerns the theoretical analysis of the evolution of these extra faces which demonstrate a very specific behaviour. In particular, they may exist and develop, growing much faster (three times) than the neighbouring faces. Despite the very high growth rates, these faces remain morphologically stable.