A very important decision for the prehistoric birdstone artisan was the selection of the material from which the birdstone was to be sculpted. The vision of the artist began with a rough stone, and the selection of that stone was carefully considered. How will this stone transform into the artistic vision of the artist? Will the natural features be capable of accentuating the line and form required of the finished sculpture? Will the selected material polish to the required sheen? Will the color be right? These were just some of the many considerations the prehistoric artist certainly considered before commencing the laborious process of creating a birdstone.

Finding the best possible raw material for a birdstone may have been a daunting task in prehistoric times. The stone must be large enough to provide the desired finished size. The importance of color and/or banding was important, as the stone must have a pleasing, desirable color or perhaps visually stimulating and perhaps strategically placed striations in the slate. Perhaps the dramatic impact of porphyry with its large contrasting phenocrysts was required for the end result. Whatever the initial requirements were, the task of finding that "just right" stone was probably a greater task than we can imagine in the 21st century.

The uncultivated eastern forests and woodlands may have made the selection process difficult. It is the speculation of the author that finding suitable raw material for the making of birdstones or other forms of artifacts would be easier today than in prehistoric times. Today it is common knowledge where large deposits of certain rock or mineral may be found. Often it is mined or collected to sell commercially. If needed, we can easily go to the sources and find it or go online and buy it. In addition, the clearing of woods and forests and the advent of mechanized farming has uncovered large deposits of rock and mineral that may have been unseen and unknown to the prehistoric artisans.

Perhaps two of the better places to find suitable stones in prehistoric times would have been creek beds and glacial kames. Creek and river beds were plentiful in the American woodlands, and access to these sources was relatively easy. Glacial kames are the large rock and gravel deposits left by the retreat of glaciers during the last ice age. These deposits were long mounds of stone and gravel that were once common in the upper Midwest. These were probably favored places to search for suitable materials for the sculpting of birdstones and the manufacture of other types of tools or weapons. In more recent times, these glacially deposited rocks and stones have been a hindrance to farming but a great, inexpensive source for building materials. Thousands of tons of gravel were taken from these gravel kames to be used for the construction of roads and railroad beds.

On a much smaller scale, I remember large rock piles on nearly every farm in northern Indiana where farmers tossed large, glacially deposited field stones that interfered with their work. Looking through these rock piles would always yield highly interesting rock specimens. In my hometown, there exists a decorative arched gateway to the city park that was made from field-found stone. Fine examples of granite, porphyry, quartz, and gneiss may be seen jutting from the concrete in which they are embedded. Similar field-stone work can be found in many fireplaces, front porch supports, and home foundations all over the upper Midwest.

Most birdstones are made from only one form of raw material, banded slate. Earl Townsend speculated in Birdstones of the North American Indian, that about 90% of all birdstones are made from banded slate. The material from which the remaining 10% of birdstones were made tends toward the exotic. Perhaps about 5% of all birdstones are made from porphyry; the remaining 5% of all birdstones would include gneiss, quartz, quartzite, pipestone, and all other known materials from which birdstones were made. Of course these percentages are estimates.

Following will be a brief discussion of the materials from which birdstones were made. Also, included (when available) will be photographs of finished birdstones made from these materials and a few examples of the raw material as it may have been found by the prehistoric artists or as fashioned into other types of artifacts.

Slate

Two samples of banded slate found in northern Indiana. The sample at left is the more commongray to green banded slate. On the right is the less common, red banded slate. Also shown are two birdstones made from green-gray banded slate. The example on the left is from Clinton County, Michigan. The example on the right is from Allen County, Indiana.

Metamorphic rock such as slate often exhibits wavy or evenly spaced bands or striations from its earlier existence as a sedimentary rock such as sandstone and shale, but it also may be found with apparently no bands or striations. Many different colors of slate may be found. In North America, gray colored slate would predominate. However, green, red, and purple slates are also noted.

What are the reasons for such a high percentage of birdstones being made from slate? First, polished slate is beautiful! The natural beauty of the contrasting bands in banded slate could also often be used to accentuate the final form of the birdstone, and this factor may be far more important than we can ever know today. It is also possible that banded slate was chosen due to its similarity to wood. Perhaps the prior experience of working with the banded structure of wood may have made banded slate a good choice. Second, slate is not as hard as quartz or granite; therefore, the pecking, polishing, and perforating process would be easier than working with the harder materials of porphyry, quartz, and granite. Third, slate may be polished to a very glossy, high sheen.

Ferruginous Slate

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 

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.