How is Quartzite formed?
Quartzite is a metamorphic rock with an ancient origin story. Tectonic activity (movement of the earth’s plates) occurring deep beneath the earth’s crust creates the heat and pressure necessary to transform a base layer rock from one form (sandstone) to another (quartzite). The resulting material has often literally moved mountains in the process of its transfiguration.
What is Quartzite?
Quartzite is a crystalline, high lustre, heavily compacted and hardened material comprising a high level of quartz as its predominant mineral component (above 90%). It registers a hardness level of 7 on the Mohs scale.
Pure quartz appears white, while quartzite stones can have a variety of tonalities depending on other ‘impurities’ present in their overall make-up. As for other natural stones, tonality and appearance will be affected by the geographic, environmental and historic circumstances of each individual stone’s creation.
Describe its Appearance and Appeal.
We often describe Quartzite as having marble-like beauty with the inner strength of granite. Unlike marble, it is not prone to etching by kitchen acids (citrus, vinegar, wine, tomatoes, ketchup etc) and, unlike granite, the hardness of its edge is visually softened by the typically more gracefully fluid appeal of its markings.
Types of Quartzite
The Three Degrees of Metamorphosis
Quartzites fall into one of three generational categories according to their degree of metamorphosis: Grainy, Crystalline and Mixed Rock. While the appearance and properties of each may vary according to the process that defines them, the primary mineral composition of all quartzites remains consistent and, consequently, all are hard, durable, and almost equally resistant to scratching and acid-based ‘etching’.
Image: White Macaubus
Grainy
At the entry level of ‘fusion’ for this metamorphic rock, we find ‘grainy’ quartzite, where some evidence of its previous existence (as sandstone) may still be just visible in a subtly grainy texture. This type of quartzite may be more porous than those further up the ‘fusion’ chain.
Grainy quartzites will require sealing to minimise porosity.
Image: Taj Mahal
Crystalline
When heat and pressure get dialled up to a next level, the grainy texture is obliterated as the sandstone grains become tighter knit, fuse entirely into each other, and take on a crystalline, glassy texture.
There are no visible grains at this level, the rock is also harder, denser and less porous than its grainy forbear. The harder the quartzite, the harder the task of a fabricator to cut it – this may also impact cost.
Mixed stone (‘Migmatite’)
Once the heat gets to a certain level, quartz begins to melt, while the impurities contained within the structure of the rock in which it is contained remain in solid form – it’s at this stage that we start to see enhanced movement between the layers as veins of pure quartz run through the body of a rock that is being compressed into tightly folding layers.
The resulting stone is a material that has been compressed into a beautiful, dense, stone with no visible or textural grain. The name ‘migmatite’, or mixed stone, describes what has now become a part metamorphic, part igneous rock that contains all the ‘extremes’ of a Quartzite – including density, low porosity, and beauty.
A Day True View
Where other stones may have better name recognition, flaunt beauty over strength (or strength over beauty), Quartzite contains the best of all worlds – it’s beautiful, durable, naturally gorgeous – if also expensive, as a result of the distance it has travelled (in time and space) and cost of fabrication.
Quartzite is, importantly, not to be confused with engineered ‘Quartz’ stones – which, while derived from the same mineral material, lack the ancestry to parallel the unique beauty of a naturally formed stone.
The sustainable credentials of any individual quartzite will depend on matters that relate to country of origin, mining, transportation and fabrication. There is no additional carbon footprint in terms of ‘manufacture’ – nature having completed the manufacture of this resource many centuries ago.
Quartzite is suited to those who are appreciative of its history and natural beauty and who are sensitive to the obligations we owe to the precious resources of our planet.
