Sand Crystals
Sand crystals are interesting examples of concretions where clusters of baryte or calcite crystals precipitate from groundwater to form as cement in unconsolidated sand. During their crystallization they incorporate the sand grains into their distinctive crystal structure. Therefore the majority of the pieces are actually made of quartz sand held in place by the mineral framework. Sand crystals usually form by evaporation in arid, sandy environments.
Baryte BaSO4
Thin tabular baryte crystals in leaf like aggregates
Size: 20 cm
Baryte Desert Rose
Sandstone concretion - a rosette aggregate of platy baryte
crystals enclosing red sand grains
Size: 25cm
Calcite CaCO3
A variety of calcite, called dogtooth spar, consisting of groupings of scalenohedral crystals resembling a dog's canine teeth
Size: 11cm
Calcite Sand Crystals
Sandstone concretion where a cement of scalenohedral calcite crystals enclose sand grains
Sample Size: 15cm (bottom)