Amygdaloidal basalt is an igneous rock which is extrusive in nature, these specimens formed over 60 million years ago during the Tertiary period and come from Ireland. They are part of the Antrim lava group and exhibit a dark colouration with occurrences of amygdales containing quartz and calcite crystals. As a basalt they are somewhat dense, but lighter than pure samples due to the cavities within them which formed as a result of gaseous activity during their ejection. Over time, hydrothermal fluids pass through the rock and minerals form within the cavities, which gives the usually dark coloured rock a speckled appearance. These samples are available in various sizes and are suitable for higher educational use to detail the subtle differences between similar igneous rocks, they come supplied in a card tray with an information label.