Cordierites

Cordierite is a magnesium iron aluminum cyclosilicate mineral. It is known for its remarkable thermal shock resistance, which makes it useful in applications where rapid temperature changes are common. The mineral typically appears in shades of blue, violet, or gray, though it can also be colorless. Its hardness is between 7 and 7.5 on the Mohs scale.

Cordierite is formed under medium to high-grade metamorphic conditions. It is commonly found in argillaceous rocks that have undergone contact or regional metamorphism. Notable occurrences include the Adirondack Mountains of New York, Finland, and various locations in Africa. It is also a primary mineral in some igneous rocks, particularly those that have undergone low-pressure differentiation.

The gemstone variety of cordierite is known as iolite, a name derived from the Greek word "ios" meaning violet. Iolite is prized for its pleochroism, meaning it displays different colors when viewed from different angles, often showing a range from blue to violet to yellowish-gray. Historically, iolite has been used as a navigational tool by the Vikings, who used its ability to determine the direction of the sun on cloudy days.

In industrial applications, synthetic cordierite is widely used in the production of catalytic converters for automobiles, ceramic filters for molten metal, and as a component in heat-resistant ceramics. Its low coefficient of thermal expansion contributes to its durability in these demanding environments. The structure of cordierite allows for the reversible absorption and desorption of water molecules within its channels, a property that has also been explored for various technical uses.