> CONCRETION – so-called “abnormal” concretions
This is a family of concretions where gravity is no longer the principal factor of development.It is replaced by:
- The microporosity of the supports
- Capillary pressure
- Surface tension
- Very reduced or intermittent flows
- Confinement
- The constraints of crystallisation
- Chemical variations in the conditions of crystallisation.
In these conditions, concretions form in defiance of gravity and take very varied forms: helictites, eccentrics, needles, sticks, efflorescences, coralloids, etc.
To these variations in the physico-chemical conditions of crystallisation, one can add concretions for which not only the crystalline forms but also the mineral composition varies in the course of their formation. So, by a process of fractional crystallisation, are formed crystals of aragonite and hydromagnesite, in dolomitic environments. |