This blue hornfels was formed by metamorphosis of a shale and greenstone (hornfelsed greenstone) source rock by a tonalite intrusion. The green hornfels from a different source rock (basalt) is located nearby formed by an earlier episode of regional metamorphism.
This blue hornfels specimen is a fine-grained rock with high hardness. Examination with a hand lens can reveal minute crystals of cuprite and garnet. Commercially this rock is crushed and used for aggregate in high-strength concrete applications such as the new runway at Brisbane Airport.
Images are examples of specimens only.
Size and shape may vary.
Specimens are usually no smaller than 75mm in one dimension.