SAGENITE AND PLUME
by Pat McMahan

Agates with inclusions are some of the rarest and most beautiful agates in the world. These inclusions may be sagenitic (sagenite), plume, dendritic, or moss. A description of each of these most common types of inclusions is important here.

Sagenite, or more accurately, sagenitic agate is any agate having acicular or needle like mineral growths. These hair like filaments are often arranged in fans or sunbursts. The inclusions come in a wide array of colors.

Plume agate has fluffy inclusions which often appear to be soft and have depth. Sometimes plume agate inclusions resemble feathers, plants, or flowers. Colors may vary as in sagenite.

Dendritic agate has thin, two-dimentional, treelike growths, usually black or dark brown, as is the case with Montana Agate. Often dendrites form between flat "waterline" bands of agate. Dendrites may also occur in limestone, talc, and sandstone, and in beryl, corundum, and other minerals.

When inclusions in agate are random in pattern, often creating the appearance of seaweed or moss, we have moss agate. Moss agate comes in many colors and is often green. Moss is the most common type of inclusion in agate.

The main focus here is on sagenite and plume agate.

I have identified sagenite from over 250 different agate deposits worldwide. My belief is that at least a little sagenite can be found at most agate fields. It is impossible to say today what percentage of the original deposits was sagenitic, but in the hundred or so agate fields I have been to, a very small percentage of the agate has sagenitic inclusions. With the exception of a small number of fields, probably less than five percent of the available agate at fields I've been to is sagenitic. Those few agate fields that have a higher incidence of sagenite offer a rare and exciting treat to the collector.

Plume is surprisingly more common than most of us might believe. Many collectors know of Priday Plume, Graveyard Point, Del Norte (Colorado), West Texas, and Mexican Plume. The oxides which form plume and other inclusions are quite common. If they are present and conditions are right, the inclusions form. I have plume from over a hundred agate fields in my collection.

Inclusions occur where iron oxide, manganese oxide, or other oxides are present when the agate is formed. The oxide minerals grow in the agate when it is in a liquid or gelatinous state. The inclusions grow and are supported by this liquid medium. If sagenite inclusions grow outside of the gel, the tops of the needles resemble a pin cushion. Plume and moss inclusions grow outside the gel as well.

In very rare instances, plume and sagenite are found in the same rock. Plume and moss are often associated together. I have found sagenite in or near moss only a few times.

Multicolor plumes appear to be more common than multicolor sagenitic sprays. I don't understand this. It may be coincidental. It is based on examining several thousand specimens. I have not yet seen plumes or sagenite needles penetrate bands in agate. My belief is that sagenite and plume are formed in silica gel after the gel fills or partially fills the cavity. Banded agate apparently forms at a different time. Some of my favorite agates have complete fortifications next to inclusions.

The thrill of finding a quality agate in the field is only topped by making that perfect, often lucky cut in the saw. Unlike banded agate which often gives the cutter multiple quality slabs, we seldom get more than one outstanding cut per rock with plume or sagenite.

As a collector, I am very selective in what I pick up in the field and still less than 5% of what I cut goes in my display case. That's the nature of what we do. A very small quantity of agates are exceptional.

As a collector, I actively buy and sell quality material. I very much like to trade material and will trade agate hunting locations.

I love to exchange ideas on hunting, cutting, and displaying. I enjoy digging and sharing a good campfire.

I can be reached at:

Phone: 928 300-8333
Email: pat@patmcmahan.com or
agates920@yahoo.com

 

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