Marble is a metamorphic rock formed when limestone is exposed to high temperatures and pressures. Marble forms under such conditions because the calcite forming the limestone recrystallises forming a denser rock consisting of roughly equigranular calcite crystals. The variety of colours exhibited by marble are a consequence of minor amounts of impurities being incorporated with the calcite during metamorphism. While marble can appear superficially similar to quartzite, a piece of marble will be able to be scratched by a metal blade, and marble will fizz on contact with dilute hydrochloric acid.
Other specimens - Click the thumbnails to enlarge
Grain size - medium grained; can see interlocking calcite crystals with the naked eye.
Hardness - hard, although component mineral is soft (calcite is 3 on Moh's scale of hardness).
Colour - variable - pure marble is white but marble exists in a wide variety of colours all the way through to black .
Mineralogy - calcite.
Other features - generally gritty to touch.
Uses - building stone; dimension stone for building facings, paving etc; cut into blocks and cut for monuments, headstones etc (wears over time due to softness of calcite, prone to acid rain damage [calcite is soluble in acid]); whiting material in toothpaste, paint and paper.
New Zealand occurrences - Northland (Marble Bay), northwest Nelson (Arthur Marble), Canterbury, Fiordland, Stewart Island.