The term ferruginous slate has been affixed to birdstones having been made from fine-grained, striated or banded material similar to banded slate but often more colorful and certainly having a higher degree of hardness. Some of the most famous birdstones known have been made from what collectors have long termed ferruginous slate. The term ferruginous indicates the material contains iron, giving the material colors tending toward reds and oranges. Indeed these colors may be quite spectacular. Townsend illustrates a few of these rare, exotic beauties in the color plates of Birdstones of the North American Indian. However, this material is more frequently found in much more subtle shades of gray, green, or black that closely resembles banded slate, as shown in the accompanying photograph of the ferruginous slate bannerstone.
This double edged or double bitted axe bannerstone is made from a very fine grained and highly polished hard slate that is commonly referred to as ferruginous slate. This bannerstone was found in Hillsdale County, Michigan.
Porphyry is an igneous rock that was a favored material for birdstone makers. Igneous rock begins life as molten magma beneath the surface of the earth. When magma finds its way to the surface it cools and becomes igneous rock. If the cooling process is quick, the crystals observed in the rock are very small. When the cooling process is slow the crystals formed are much larger. These crystals are commonly termed phenocrysts. Many forms and colors of porphyry are found around the world. Very large phenocrysts set in a contrasting matrix of dark green granite was apparently the type favored by prehistoric birdstone makers. This type of material is shown in the photographs below. Many birdstones made from porphyry do not display such large and showy phenocrysts, but the material is still usually dramatic and quite beautiful.
Many of the more highly developed birdstones are made from porphyry and these are among the most highly sought after by collectors. The material is showy and beautiful, and if not weathered too much over the centuries, the degree of polish can be amazing. A saddle birdstone with popeyes and a fantail would be a great example.
This ntgnty pannarea, targe porpnyry cobble was purposely broken into two portions. It was originally found in Michigan and has a maximum circumference of 19″.
This photograph illustrates the interior view of the same porphyry cobble, along with two birdstones fashioned from porphyry similar to the cobble. The birdstone on the left is from Alpena County, Michigan. The birdstone on the right was found in Allen County, Indiana.
Granite is a very common igneous rock. Like porphyry, granite began as molten magma beneath the surface of the earth, and after emerging on the earth’s surface, it cooled rather slowly, crystallizing into one of several types of granite including pink granite, white granite, porphyritic granite, and hornblende. However, the crystals formed in granite tend to be smaller and less showy than in porphyry. Granite was also a favored material for the manufacture of prehistoric stone tools. Beautiful, highly polished and colorful axes and celts abound.
This photograph illustrates a saddle birdstone made from black and orange granite. It was found in Will County, Illinois.
There appear to be far more porphyry birdstones than there are granite birdstones. Like porphyry, granite would have been rather difficult to work. Nearly all forms of birdstones, including chunky birdstones, have been made from granite. Many of these are highly polished and a few are highly developed. Colors of granite birdstones vary widely with green, tan, orange, and golden colored granite being the predominate colors used. It is also interesting to note that common pink granite was never used.
Like slate, gneiss (pronounced “nice”) is a metamorphic rock often having quartz and feldspar inclusions. This mixture of different types of rock was formed underground by high heat and high pressure. Gneiss is characterized by inclusions that often form definite striations or banding. These bands may range from black to green to white. Birdstones made from gneiss may have a highly polished glossy appearance, or they may be highly weathered or pitted as gneiss Appears to weather more easily than do slate or granite. This is probably due to being in acidic soils. These birdstones may have a definite coloration or patina depending on the material with which it may have been in contact, such as red ocher. Various soil types may also play a significant role in the present coloration of birdstones made from gneiss which are often tan in color. Gneiss was a favored material for the makers of bust birdstones. Earl Townsend identified a number of gneiss bust birdstones.
These three stones are made from gneiss. From left to right: This birdstone made from gneiss was probably once in contact with red ocher or ground hematite. Although the provenience has been lost, this birdstone was most likely found in Ohio. Bust birdstone found in Clinton County, Ohio, Featureless bust birdstone found in St. Clair County, Illinois.
Quartz is a very hard mineral. Like other minerals, quartz is elemental. In other words, a sample of quartz is basically just quartz. When fractured, quartz may be seen as hexagonal prisms that are topped by pyramid-like shapes. Some types of quartz are smoky quartz, rose quartz, amethyst, rock crystal, citrine, and milky quartz. Although many bannerstones have been found that are made from pink to red to orange colored rose quartz, the makers of quartz birdstones seemed to prefer milky quartz.
This quartz birdstone is made from translucent quartz. It was found in Randolph County, Indiana.
Quartzite is a very hard metamorphic rock that began its existence as sandstone. Due to very high heat, high pressure, and time, the individual quartz grains of the sandstone re-crystallize This process erases all of the original sedimentary qualities of the original sandstone. Quartzite is usually white to gray in color, but red, pink, and orange may also be seen. No artifact examples of quartzite were available for illustrative purposes.
Another rare material for the construction of birdstones was Catlinite. Artifact collectors generally refer to Catlinite as pipestone. Catlinite/Pipestone is a type of metamorphic rock known as argillite or metamorphic mudstone. Pipestone quarries and deposits exist in Minnesota, Ohio, Illinois, New York, Canada, and probably several other locales. It is very soft when first mined and may easily be carved or abraded. Pipestone birdstones are highly polished and often animal in form. Many pipestone artifacts have been found in a wide variety of colors ranging from gray, tan, yellow, red, and pink.
Five pipes, one gorget, one pendant and one birdstone made from various colors of pipestone from various sources. The animal form birdstone resembling a bear is made from tan-yellow pipestone and is from Crawford County, Ohio.
Birdstones made from the following materials are extremely rare. However, one or more authentic examples have been noted in the literature; therefore, mention of these materials is in order.
Sandstone is a very common sedimentary rock that was formed by layers of fine particles of quartz sediment that over long periods of time and pressure became sandstone. Sandstone is usually found in many shades of tan or brown, but many other colors exist. Townsend notes a few sandstone birdstones as being found in the State of New York.
Corals are simple marine animals that often live in colonies attached to the sea floor. They have a hard exoskeleton made from calcium. Large deposits of these ancient fossilized sea animals may be found all over the world. When fossil coral is polished, it has a very glossy, glass-like finish that is quite beautiful. Only one authentic fossil coral birdstone has been noted, and it has weathered considerably over time. However, in its original prehistoric condition, it was certain to have been very smooth and highly polished.
Typical birdstone made from highly weathered fossil coral. This birdstone was found in Rock County, Wisconsin. Illustrated behind the birdstone is a small sample of fossil coral found in Indiana.
Limestone is a sedimentary rock that was formed from large deposits of ancient marine life such as coral. Limestone is often white in color but may take on many other shades of color during the patination process. Very few limestone birdstones have been found, but a few have been noted. None were available for illustrative purposes.
Cannel coal is actually a type of coal found at the top or bottom of coal deposits. Prehistoric artisans often made beautiful, highly polished gorgets, pendants, and many other types of prehistoric artifacts from cannel coal. It is very light and may be easily carved and easily polished. Townsend notes only two birdstones made from this material, and one of them may actually be an entirely different type of artifact.
Steatite is metamorphic rock that is also known as soapstone. The major component of steatite is the soft mineral talc. Townsend notes in his birdstone book that a few steatite birdstones have been found along the East Coast of the United States.
Illustrated here is a historic steatite Micmac pipe from Montgomery County, Ohio.
Hematite is a mineral form of iron. It may be black, silver, brown, red-brown, or red. Many prehistoric artifacts have been found made from hematite, but only one or two authentic birdstones have been noted in the literature as being made from hematite.
On the left is a highly polished hematite cone showing the polished silver/black coloration of hematite. On the right is a large prehistorically worked round ball of hematite showing the brown-red coloration of hematite.
Note: All of the birdstones, other artifacts and most of the material samples illustrated with the above article are from the collection William S. Koup, Albuquerque, New Mexico. The exceptions are the gray pipestone gorget illustrated with Catlinite/Pipestone and the quartz birdstone on page 33, which are from private collections.