A large class of materials are known to transform from a crystalline to an 
amorphous structure under pressure changes at constant temperature. Among 
others, typical materials are water (H2O), quartz (SiO2) and berlinite 
(AlPO4). 
One of the striking  (though rather controversial) properties observed in 
some pressure-induced amorphous materials is the so-called memory glass 
effect: when the amorphous sample is decompressed, the initial crystalline 
structure is recovered, conserving the original crystal orientation.

Here, a model of interacting particles in two dimensions is studied in 
order to address some issues related to pressure induced amorphization and 
the memory glass effect. Two limit scenarios are presented according to the 
nature of the mechanical instabilities underlying the transformation: a direct
crystal-to-amorphous transformation and a martensitic transformation. In 
the last case the product phase can be a poly-crystal with a very small 
grain size and the material can be easily taken as an amorphous material. 
The memory of this \"amorphous\" structure is a natural consequence of the 
underlying martensitic transformation.