The Gods of Rock: Pluto and Vulcan

Human beings have been working stone for a long time. It seems as though physically our hands and bodies are perfectly adapted for the task. Likewise, the ability to conceptually form stone into tools, hunting implements and structures might well be hardwired into our DNA. Such an enduring material, much of what is gleaned of early civilisation in the field of anthropology has quite literally been recorded in stone. This post initiates a three part series to shed a bit of light on the types of stones that generations of masons and carvers have found most useful. 

We Have Ignition!

We'll begin with what are called primary rocks*, so classified because they are the direct result of the original consolidation of minerals into stone. The common name for this group of stone is Igneous, derived from the Latin "Ignis" meaning "fire". That name is a strong indication of the origin of Igneous rocks, deep under the earth's surface in the lower crust or even the mantle. Oxidized silicon compounds (silicas, SiO2 or silicates, SiO₄) under extreme heat and pressure form and mix  into a liquid, molten state known as magma. How that molten magma cools distinguishes the two major sub-classifications of igneous rock.

Pluto - God of the Underworld...

and Riches

Most folks know Pluto as the counterpart of the Greek Hades, the Roman god of the underworld. However, the Romans had a more positive view of Pluto also considering him the god of wealth, a giver of abundant riches. This was in no small measure due to the mineral wealth the Romans were particularly adept at unearthing from mining operations. 

Plutonic rocks are Igneous rocks that have specifically cooled, underground within the earth's crust, surrounded by other rocks. The other rocks act as a kind of insulation. As a result Plutonic rocks cool very slowly. This allows time for large and long crystal formation, resulting in a coarser textured stone. Plutonic rocks are also classified as Intrusive rocks because the magma typically "intrudes" or fills horizontal or vertical strata known as "sills" and "dikes" respectively. Larger cooled magma chambers can produce "bathotliths", huge massifs that can account for entire mountain ranges.

The most common form of Plutonic stone used for masonry is granite. Although coarse, brittle and hard to work, granite is a beautiful stone that is exceedingly durable. Because it is hard to achieve fine detail it is best reserved for large scale, monumental work when carved.

Vulcan - God of Fire...

and Volcanoes

What is not commonly known is that Vulcan was also the god of metalworking specifically and crafts in general. Most often in ancient sculpture you'll find him hammer in hand surrounded by billowing fire and smoke. The stone temples of the gods were attributed to the hands of Vulcan. 

Volcanic rocks are also Igneous rocks; however, volcanic rocks are formed from lava, magma that has been discharged from underground into the sea or in the open air. Therefore, volcanic rocks are classified as Extrusive rocks as they are "extruded" as lava from underground magma tubes onto the surface where they rapidly cool. There are many varieties of useful volcanic rock for masonry and carving. Basalt in particular shares the density and durability of granite. Yet, because of the rapid cooling, the crystalline structure basalt is much smaller and finer allowing for greater detail in carving. The Giant's Causeway on the coast of Ireland is an amazing example of a volcanic basalt formation popularized by rock gods Led Zeppelin on the iconic cover of their Houses of the Holy album.

Next in the series we'll consider my personal favourite for carving, sedimentary stone.

*The terms "rock" and "stone" are used interchangeably in this post. Some consider "rock" to denote the natural form whereas "stone" is distinguished by or set aside for human alteration.

Contributed by Patrick Webb