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Identifying Mammoth Ivory

Discussions, identification and analysis of Mammoth Ivory
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souldeep
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Identifying Mammoth Ivory

Postby souldeep » Mon Mar 28, 2016 4:17 pm

Identifying Mammoth Ivory - Mammuthus spp.

Mammoth tusk ivory comes from the two modified upper incisors of extinct order (Proboscidea).

Mammoths have been extinct for 10,000 years. Because of the geographical range in Alaska and Siberia, Mammuthus primigenus tusks have been well preserved. Therefore, Mammuthus primigenus is the only extinct proboscidan which consistently provides high quality, carvable ivory.

Enamel is only present on the tusk tip in young animals. It is soon worn off and not replaced. Whole cross-sections of proboscidean tusks are rounded or oval. Dentine composes 95% of the tusk and will sometimes display broad concentric bands. Cementum, which can be thick in extinct genera, covers the outside of the tusk. Cementum can present a layered appearance, particularly in mammoth.

Polished cross-sections of Mammoth ivory dentine display uniquely characteristic Schreger lines. Schreger lines are commonly referred to as cross-hatchings, engine turnings, or stacked chevrons. Schreger lines can be divided into two categories. The easily seen lines which are closest to the cementum are the outer Schreger lines. The faintly discernable lines found around the tusk nerve or pulp cavities are the inner Schreger lines. The intersections of Schreger lines form angles. These Schreger angles appear in two forms: concave angles and convex angles. Concave angles have slightly concave sides and open to the medial (inner) area of the tusk. Convex angles have somewhat convex sides and open to the lateral (outer) area of the tusk. Outer Schreger angles, both concave and convex, are obtuse in extant proboscidea.

A photocopy machine is used to capture Schreger angles from mammoth and elephant ivory cross-sections. The cross-section is placed on the glass plate of a photocopy machine. A blue photocopy transparency sheet may be placed between the object and and the glass plate to enhance the detail of the photocopy. Enlargement of the photocopy may also improve the image and facilitate the measurement process.

After a photocopy of the ivory cross-section has been obtained, Schreger angles may be marked and measured. Use a pen or pencil and a ruler to mark and extend selected outer Schreger angle lines.

NOTE: Only outer Schreger angles should be used in this test.

Once the angles have been marked and extended, a protractor is used to obtain an angle measurement. Several angles, including both concave and convex angles, should be marked and measured. Once the angles have been marked and measured, calculate the angle average.

Because specimens from both extinct and extant sources may present angles between 90 degrees and 115 degrees in the outer Schreger pattern area, the differentiation of mammoth from elephant ivory should never be based upon single angle measurements when the angles fall in this range.

When averages are used to represent the angles in the individual samples, a clear separation between extinct and extant proboscideans is observed. All the extinct proboscideans had angle averages below 100 degrees.

mammsmal.jpg

Another feature may be used to identify mammoth ivory. Mammoth ivory will occasionally display intrusive brownish or blue-green colored blemishes caused by an iron phosphate called vivianite.
Piglet: "Pooh?" Pooh: "Yes, Piglet?" Piglet: "I've been thinking..." Pooh: "That's a very good habit to get into to, Piglet." - A.A. Milne.

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