Limestone Microcrystalline limestone that forms in warm, shallow seas through precipitation of CaCO3 from sea water Size: 10cm Oolitic Limestone Cemented rounded grains of CaCO3 rolled by sea-bed currents (oolites) Size: 10cm Dolostone A chemical sediment containing the mineral dolomite CaMg (CO3)2 formed secondarily by Mg-replacement of limestone Size: 10cm Rock gypsum Forms dominantly by the evaporation of sea and lake water in arid environments Left: 8cm Right: 12cm Ulexite NaCaB5O9. 8H2O Called TV-Stone due to its unusual fibre-optical effect of transmitting images through the closely-packed parallel fibrous crystals Size: 5cm Phosphorite Nodule Marine deposit with high concentration of phosphates in a nodular mass typically found in shallow marine environments beneath upwelling surface waters Size: 10cm