Name: Basalt
Description: Fine grained, sometimes glassy rock formed when lava cools very quickly
Colour: Grey, brown, black

Name: Chalk
Description: Fine, powdery, soft limestone            
Colour: White

Name: Conglomerate
Description: Pebbles and gravel held together by hard sand or clay
Colour: Mixed

Name: Granite
Description: Fine grains of quartz and other minerals locked together
Colour: Mottled white, grey, pink, red

Name: Limestone
Description: Made of calcite (calcium carbonate) and fossil remains
Colour: White, grey, cream, yellow, brown

Name: Marble
Description: Smooth rock, formerly limestone, which can be polished
Colour: Often white but can be various colours including green

Name: Obsidian
Description: Natural glass formed in lava flows  
Colour: Dark grey, red, brown, black

Name: Slate
Description: Fine-grained rock that splits easily, used as a tiling material
Colour: grey, blue, green, brown, black

Name: Sandstone
Description: Sand grains packed tightly together
Colour: white, yellow, grey, green, brown