Change You Can Believe In

Apollo and Daphne, Bernini

“What you leave behind is not what is engraved on stone monuments, but what is woven into the lives of others.” ― Pericles

Metamorphosis: the changing of form of one thing into that of another. Bernini effectively captures the moment of metamorphosis of the nymph Daphne. Her pleas answered, she is transformed into a tree, escaping the lustful pursuit of the god Apollo. Yet Bernini's work too is a metamorphosis: that of a block of lifeless marble transformed into a frozen moment of movement and emotion. Underlying all of this is yet another transformation, that of the marble itself, belonging to a third or tertiary group of rock classified as Metamorphic.

Marble

Marble starts off its existence as a sedimentary rock, limestone. Through heat and pressure within the earth's crust its molecules are loosed from their bonds. Subject to magnetic forces they reorient, align becoming more crystalline. If the limestone is pure the marble will be an unadultered white such as the Luna marble used for Benini's sculpture. More often the limestone has impurities of sand, clay or other minerals that can provide interesting patterns of veining as well as a large variety of colours, many quite vibrant.

Rossa Verona marble, Basilica di Santa Maria Maggiore a Bergamo

Slate

Charleston, SC

Under certain conditions clays composed of quartz and mica will settle in sedimentary beds that later undergo compaction. These form leaves of shale, a very fissible or flaky stone not typically useful as a building material.  Under given conditions of heat and directional pressure shale will transform into slate. One of slate's most useful qualities is its impermeability of water absorption. This makes it ideal for water tables and as a roofing material. Although most slate occurs in darker colors there is still considerable variety that allow for intricate pattern making. As a result slate roofs can be quite beautiful, require minimal maintenance and often last hundreds of years. Despite its hardness and density, slate is very finely textured which makes it a desirable, enduring material for plaques and gravestones.

Quartzite

Amenhotep III, Thebes

As limestone will transform into marble, sandstone subjected to similar conditions will change into quartzite. It completely loses its original sedimentary character ending up with a very homogeneous texture. The resulting stone is typically extremely hard and likewise phenomenally durable. Quartzite is often used for paving of roads because of its character. The ancient Egyptians used quartzite for colossal monumental work. Many of their original statues have endured the elements in good condition for thousands of years.

Schist and Gneiss

Unlike the aforementioned, schist and gneiss are classifications of rocks that have undergone a geological process independent of their chemistry. They are more often than not a fusion of several different types of rock that have become subject to extreme tectonic forces, such as those occurring at continental plate boundaries. These forces causes the minerals in the rocks to separate and begin to form independent layers. Schists have varying degrees of hardness but are characterized by 'foliation' referring to fine layers that can be easily split. Gneiss by contrast is not easily split at the coarser layer boundaries and tends to be a much harder material. Gneiss is a very common material making up a large percentage of the bedrock of the earth's crust.

Gal Viharaya Buddha

That concludes this brief series on the three main classifications of rock: Igneous, Sedimentary and Metamorphic. I hope you've enjoyed them! Meanwhile, it's time for me to get back to carving. Look forward to updating you on my next project, a Jacobean fireplace in limestone.

Contributed by Patrick Webb