The photo shows a Lithophone made of shiny, black and very hard
rock taken from Blencathra on Skiddaw. Each note of the
Lithophone is carved out of a single piece of rock called
Hornfels, a metamorphic rock.
Metamorphic rocks make up only 2% of the earth’s crust.
Metamorphic rocks are formed by heat and pressure. When
continents collide sedimentary rocks are put under great heat
and pressure. This is called regional metamorphism. The clays
and silts of Skiddaw were squashed into slates when two halves
of our country joined at the end of the Silurian Period.
Granites were injected into the crustal junction causing contact
metamorphism. The rock surrounding the granite was baked at
600-700 degrees centigrade. Rings of metamorphic rock change,
called Aureoles, surrounded the granite, with the lowest
temperature rocks furthest from the granite. The highest grade
rock (Hornfels) was closest to the granite.
The original slate, closest to the granite, was baked at very
high temperatures for about a million years. The slate structure
and crystals were completely destroyed in the baking process.
The Hornfels that formed were made out of small, interlocking
uniform crystals. The texture of this new rock is described as
It is likely that the uniform crystal texture gives the rock
it’s ”ringing” sound when the rock is struck with a hammer.
Lithophones of Hornfels took a long time to construct because
the Hornfels were so hard and difficult to work. The Keswick
Lithophone stones took over six months to cut and tune.