Articles

A Porphyry Granite Celt

Non-grooved stone axes, also known as celts, were used by the natives in North America for many thousands of years for general wood cutting and also probably for warfare.  These ancient people used whatever hard stone was available for these tools but more often than not, the plain mineral granite was chosen since it was so tough, would hold a good cutting edge and was very abundant.  And on more rare occasions, the prehistoric tool maker chose an uncommon type of granite such as was used for this porphyry granite celt.

Granite is a felsic igneous rock that was formed intrusively (meaning below the Earth’s surface) from super-heated molten stone or magma.  It is found throughout the world and is considered to be Precambrian in age which means it predates the emergence of life in the Cambrian Period or 600 + million years ago.  It is primarily composed of quartz, feldspar, hornblende and mica but will usually contain small quantities of other minerals.  Granite, from the Latin word “granum” meaning “in grain”, is a coarse grained rock that has crystals or phenocrysts large enough to be seen with the unaided or naked eye.  Scientists call it “crystalline siliceous rock” which means it is comprised of various crystalline inorganic compounds from the silicate mineral family.  Some geologists also state that granite is only found on the planet Earth but one must wonder just how they deduced that bit of superfluous information.  All granite includes quartz and feldspar but since most granite magma cooled at a steady rate below the surface, all the mineral particles contained within the rock are about even in size and texture.  But some granite magma cooled at more than one rate of time thus causing some of the minerals incorporated within to solidify more quickly while others remained in a molten state for a longer period.  Porphyry granite is one of the rock types that falls into this multiple cooling rate category.  The matrix is certainly common multi-mineral granite but some of the quartz or feldspar inclusions cooled more rapidly and thus formed into crystals which now show up as small hunks of stone imbedded in the granite substrate.  Feldspar, itself, is a tectosilicate which is a rock-forming mineral.  The name comes from the German words “feld” meaning field and “spar” meaning light colored mineral that cleaves with a smooth surface.  Feldspar is found in all three mineral types, igneous, metamorphic and sedimentary and composes about 60% of the Earth’s crust worldwide.

The celt pictured with this article was found in Yadkin County, North Carolina many years ago.  It is a typical early square sided un-grooved axe type that was probably made in the Late Archaic to Early Woodland Periods or 3,000 to 500 BC.  Stone celts were made by the prehistoric Americans from perhaps as early as 8,000 BC until the eighteenth century AD when they were supplanted by iron axes traded by the early Europeans.  They were made alongside the larger grooved stone axes for thousands of years but we do not know just why the ancient people chose to make and use both the grooved and un-grooved cutting utensils during the same time periods.  This celt is 5 7/8” in length and the bit is well polished from usage and from many re-sharpenings from its original larger size.  It is made of typical grey granite that is found throughout the Piedmont and mountains of the Tar Heel state but it is also atypical because it contains many large feldspar phenocrysts.  These irregularly shaped feldspar inclusions range in size from about 1/8 inch across to as large as ¼ inch by ½ inch in size.  Feldspar is normally in the range of a 6 on the Mohs mineral hardness scale which means it is compatible with the hardness of granite matrix which is normally around a 7 on the same scale.   Celts made of porphyry granite are quite rare in the Piedmont in spite of the fact that North Carolina is the leader in feldspar mined in our country and is also a major producer of granite with that mineral being named the official state rock.  With an abundance of feldspar and granite, one would think that many more anciently made porphyry granite stone tools would be in existence, but they are very infrequently found.   Porphyry granite stone axes, grooved or non-grooved, are in fact not common anywhere in the United States and are highly prized by modern collectors.  One would certainly wonder if the ancient tool maker did or did not know that the piece of granite he began working with to produce this celt contained the large feldspar phenocrysts.  Or did he even care since it was simply a necessary daily use cutting tool – not an object of art.  But he did indeed create an object of art.  He created a rare and attractive specimen of ancient stone tool making that he would have simply called a cutting instrument but today would be called an unusual and beautiful porphyry granite celt.

 

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