Louisiana palm: An oval cabochon cut from Louisiana palm. The face of the cabochon was cut parallel to the trunk of the palm. The lines represent the vascular structure of the plant. The cabochon is about 57 x 33 millimeters in size.
Louisiana palm: A round cabochon cut from Louisiana palm. The face of the cabochon was cut perpendicular to the trunk of the palm. The dots are cross-sections through the vascular tubes of the palm. The cabochon is about 29 millimeters in diameter. The Louisiana palm cabochon at the top of this page and the one immediately above were cut by Tom Wolfe of Wolfe Lapidary.
"Petrified palm": An oval cabochon cut from Louisiana palm with three colors of chalcedony. This stone measures about 40 millimeters x 30 millimeters in size.
Louisiana "Palm Wood"
The most widely known Louisiana gem material is the Oligocene-age "petrified wood" that is found in the Catahoula Formation,
a sedimentary rock unit that was deposited on the alluvial plains and in the coastal swamps of the Oligocene Gulf Coast. At that time, the coastline was about 100 miles farther inland than it is today. Sediments shed, mainly from the uplift of the Rocky Mountains, have since built the coastline seaward to its current position.
Most specimens are a palm of the genus Palmoxylon, which has been named as the state fossil of Louisiana. Palmoxylon did not produce a true "wood" composed of cellulose and lignin. Instead it was a plant that looked similar to a modern palm
tree with a trunk made up of parenchyma, a fibrous support material that surrounded hollow tubes of the plant's vascular structure
known as xylem and phloem. These tubes transported water, nutrients, wastes, and other materials through the plant.
When the palm died, it had an opportunity to be preserved as a fossil if it was quickly covered by water and sediments that
would protect it from oxidation and destructive organisms. Ground water flowing through the sediments carried dissolved
silica that sometimes precipitated within the hollow xylem and phloem to preserve them. The silica would also replace the
fibrous parenchyma. This infilling and replacement of the plant structures with solid silica produced the fossil known as
Today, fossilized palm trunks and fragments are found at many locations in Louisiana, Texas, and Mississippi, where the Catahoula Formation is exposed at the surface. Pieces of this material that are completely and uniformly silicified are often of high enough quality to be cut, polished, and used as gems. It is also used to make small sculptures, spheres, book ends, and other ornamental objects.
When the material is cut along the length of a palm trunk, the tubes of the vascular structure often have an appearance that
resembles wood grain. When it is cut perpendicular to the palm trunk, the tubes of the vascular structure often display as an
array of "dots." Cabochons cut from wood slices sawn in these orientations are shown in the photos above.
Louisiana palm fossils can be colorful. They typically range in color from white to honey brown or from chocolate brown to
black. Red, orange, and pink colors are also found. The material is usually a chalcedony, but some occurrences of opalized palm are known.
"Petrified palm" is an attractive material that represents a time in the geologic history of Louisiana. It is also
attractive enough and abundant enough to be widely known, and for those reasons it was named as Louisiana's state fossil.
Louisiana opal: A square cabochon cut from sandstone found in Vernon Parish, Louisiana, that is cemented with precious opal. A play-of-color is produced by the interstitial cement when the cabochon is moved under incident light. The cabochon measures approximately 20 x 20 millimeters in size.
Small amounts of a material called "Louisiana Opal" or "Louisiana Sand Opal" have been mined from the Catahoula Formation near
Leesville, Vernon Parish, Louisiana. If you examine this material closely, you will find that it is a
sandstone in which the sand grains
are bound together by a cement of clear precious opal.
When this sandstone is completely cemented, solid, and unweathered, it is stable enough to be slabbed, cut into cabochons, and polished to
a bright finish. When a polished cabochon is played in incident light, the interstitial opal can produce small patches of play-of-color.
The material is not spectacular in appearance, but it is a genuine precious opal. It is a novelty gem that is enjoyed by local people
and gemstone collectors. Small amounts of this material were produced in the late 1980s and early 1990s. It is no longer produced, and
rough material is difficult to find.
In addition to cabochons, lapidarists have used Louisiana Opal to produce spheres and other
objects. Most of the material has a brown base color like the 20mm x 20mm cabochon shown in the photo above. It also occurs with a gray
to black base color. The play-of-color is much easier to see in specimens with the darker base colors.