Calcite on Limestone
The associated card describing this specimen lists it as "crystals coated with calcite on limestone." Looking around the interweb it may be that the crystals are calcite rather than "coated with", but maybe that wasn't known when the item was acquired. It comes from Alston in Cumbria, which is south-east of Carlisle and situated in the Pennines.
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). Polymorphs are the various forms or crystal structures that can be created from the mineral. Aragonite and vaterite are the other polymorphs of this mineral but they both change to calcite in a matter of days or less.
Calcite is perhaps one of the oldest names for a mineral. It was given its name by Gaius Plinius Secundus, better-known as Pliny the Elder, in 79 AD. The name comes from Calx, which was Latin for lime.
A very common and widespread mineral with highly variable forms and colours, calcite is best recognised by its relatively low hardness and its high reactivity with even weak acids, such as vinegar.
Over 800 forms of calcite crystals have been identified. Ancient Egyptians carved many items out of calcite, relating it to their goddess Bast, whose name contributed to the term alabaster because of the close association. In the 21st century, experiments have been conducted to use calcite for a cloak of invisibility!
The specimen seen above can be found in the Minerals section of the Natural History Museum in South Kensington, London. It is about 75cm on its long axis.
Calcite on Limestone
The associated card describing this specimen lists it as "crystals coated with calcite on limestone." Looking around the interweb it may be that the crystals are calcite rather than "coated with", but maybe that wasn't known when the item was acquired. It comes from Alston in Cumbria, which is south-east of Carlisle and situated in the Pennines.
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). Polymorphs are the various forms or crystal structures that can be created from the mineral. Aragonite and vaterite are the other polymorphs of this mineral but they both change to calcite in a matter of days or less.
Calcite is perhaps one of the oldest names for a mineral. It was given its name by Gaius Plinius Secundus, better-known as Pliny the Elder, in 79 AD. The name comes from Calx, which was Latin for lime.
A very common and widespread mineral with highly variable forms and colours, calcite is best recognised by its relatively low hardness and its high reactivity with even weak acids, such as vinegar.
Over 800 forms of calcite crystals have been identified. Ancient Egyptians carved many items out of calcite, relating it to their goddess Bast, whose name contributed to the term alabaster because of the close association. In the 21st century, experiments have been conducted to use calcite for a cloak of invisibility!
The specimen seen above can be found in the Minerals section of the Natural History Museum in South Kensington, London. It is about 75cm on its long axis.