Articles

STONES USED BY PIEDMONT INDIANS - PART III

This will be the last segment that will discuss the various stone materials used by the prehistoric to historic period Indians in the Carolinas and Virginia.  In this part, the discussion will be about one of the more common rocks, porphyry, which can be a misnomer as you will see and also two less common minerals, sandstone and limestone.

Porphyry

Technically the word porphyry can be a noun describing a type of stone or an adjective that precedes or supersedes the name of another type rock.  Porphyry, geologically speaking, is a type of igneous rock that is made of large grain and distinct crystals, especially alkali feldspar, dispersed and imbedded in a coarse to fine-grain matrix.  Igneous rocks are essentially heated or volcanic minerals and were formed intrusive and extrusive to the earth surface.  The word igneous, of which there are over 700 variations worldwide, comes from the Latin word igneus which means fire thus relating to this rock being formed by extreme heat.  It was super heated underground, usually by volcanic action, and was formed millions of years ago by slow lava flow or by violent volcano eruptions.  Of course, this can still happen today if an active volcano decides to blow its top.

The word porphyry is derived from the Latin word porphyres which means purple.  It was initially named porphyry because of the purple granite porphyry used by the ancient Egyptians in their buildings and statuary but today refers to the texture of igneous rocks containing large grain crystals, regardless of color.  Stone porphyry was, and still can be, formed from slow cooling and solidification of liquid rock.  It always has a uniform texture without layering and it has mineral grains or phenocrysts packed tightly within the groundmass.  These phenocrysts (feldspar, quartz, mica, etc) solidified more quickly than the remainder of the rock which make them more visible to the naked eye.

In the Piedmont and surrounding areas, stone porphyry is coarse grained and intrusively formed (such as granite and diorite) or fine grained and extrusively formed (such as basalt, andesite or rhyolite).  These rocks came from the geologic region that today we call the Uwharrie Mountains which were volcanoes millions of years ago.  The prehistoric inhabitants of the region certainly had access to these minerals and used them to make tools and decorative ornaments.

In written material and vocal language, Indian artifact collectors regularly use the word porphyry to describe a particular stone.  While this is not actually incorrect, the more proper description would be to name the stone (granite, rhyolite, etc) and precede or follow that rock name with the word porphyry, such as porphyry rhyolite or granite porphyry.  By using only the name porphyry, one will not know exactly the stone in which the porphyritic minerals are embedded.  Porphyry rhyolite is very common and porphyry granite is reasonably common in the Piedmont.  Some other porphyritic stones, such as porphyry diorite, porphyry basalt and porphyry andesite are rarer but have certainly been found in the region.  So if you find an Indian artifact that clearly shows large crystals in the matrix, attempt to define the matrix or base rock before you simply call the stone porphyry.

Sandstone

Sandstone, as the name implies, is a material composed of sand sized mineral grains usually 1-2 mm or less across.  It is made of mostly of quartz and feldspar sand and comes in about every color known but primarily is tan, yellow, white, grey, brown and red.  Sandstone is a clastic mineral meaning it is not composed of organic substances.  It was formed at least 500 million years ago in two ways, the first of which was the accumulation of sand grains in the bottoms of lakes and seas that became compacted and cemented by precipitation of other minerals, such as calcite, clay and iron oxides, between the sand grains.  The other method of sandstone production was when the dry sand grains were blown by the wind and deposited in layers and went through a similar compaction and cementing process.  The hardness of sandstone depends on the actual sand type and the cementing substance but generally falls in the 5 to 7 range on the MOHS mineral hardness scale.

Sandstone is a common mineral in many parts of the world.  In the western part of the USA, there are mountains of red/brown sandstone that were cut and moved to large eastern cities in the late nineteenth and early twentieth centuries to build the famous “brown stone” buildings.  It is not so common in the Carolinas and Virginia but is certainly here in limited amounts.  It was most commonly employed by the ancients, in the region, for use as abrading tools to smooth spear/arrow shafts and other wooden tools.  It was also used to grind the lower edges and bases of spear points so the material that bound the stone to the shaft would not be cut.  Sandstone was also occasionally used in smoking pipes, bannerstones, ear spools and other ornaments.  Even though sandstone is found in a multitude of colors, most of the Indian artifacts recovered in the Piedmont, are dark tan to brown to red.  Artifacts made of this mineral are rare in this region but they can be found and if you discover a small roughly textured tool, especially with one or more grooves cut into it, you have probably discovered an ancient abrader made of Piedmont sandstone.

Limestone

Limestone is a sedimentary rock composed primarily of the mineral calcite.  It was formed millions of years ago by the settling of calcite containing minerals in the sea bottoms to make “white mud” and/or the settling of dead marine animal bodies and shells (which are composed of calcium carbonate or calcite) into the ocean floors.  As the water evaporated with the continental formations, this sea ooze and deceased marine life compacted and hardened to form limestone.  Our name for this mineral comes from the Greek word for lime, Chalix and is found throughout the world in the colors of white, tan, yellow, brown and black.

As collectors of Indian artifacts in the Piedmont, we do not think of limestone as being a material used by the ancient people but it was.  This dry land on which we now live was the ocean bottom millions of years ago and the limestone that was formed is still here.  With a hardness of around a 3 on the MOHS hardness scale, this soft stone was easily carved into pipes, pendants, bannerstones and bowls.  Most of these artifacts will be white to grey to brown in color and the texture will usually be very fine grained and may have a chalky look and feel.  It is not at all rare to find limestone artifacts that clearly display small fossilized marine shells or holes that were left after the shells leached away.

Even though limestone is relatively soft, it is still a material that can and has withstood the wrath of nature.  Many ancient cultures used the mineral as building materials and many of these structures, such as Mayan pyramids in Mexico and Central America, have withstood the millennia reasonably well.  While Indian artifacts made of this material are not common in the Carolinas and Virginia, they can be and have been found.  They are easy to identify with the white/grey/brown colors and chalky feel – these unique relics of a bygone era made of the ancient sea born limestone.