Ironstone Vineyard's Heritage Museum now features and outstanding collection of petrified wood.
Visit free of charge, the collection is located just outside the Heritage Museum & Gift Shoppe.
PETRIFIED WOOD COLORS
M.P. Hunerlach, 2016
Which minerals produce the colors found in the
petrified wood?
Red and Pink colors are produced by the presence of hematite, a form
of oxidized iron - Fe2O3. The intensity of the color
depends on the quantity of hematite present in the petrified wood.
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Process:
Iron dissolves in ground water when no oxygen is present. The ground water
becomes re-oxygenated as it moves though the tree trunks causing oxygen to bond
with the iron. The iron then precipitates to produce a solid form of iron
called hematite. This hematite is incorporated into the log's cell walls. The
same process occurs when iron stains porcelain sinks. The soluble iron in
ground water becomes oxidized into a solid form when it comes in contact with
air, causing a reddish stain.
Yellow, Brown and Orange colors are produced by the presence of
goethite - HFeO2 and Fe2O3. Goethite is a
hydrated iron oxide that is derived by weathering from iron bearing minerals.
It crystallizes into tablets, scales, needles, radial and concentric
aggregates.
Green colored petrified wood is produced by pure reduced iron that is
a magnetic, malleable mineral. The chemical composition is Fe. Referred to as
native iron, it is quite rare in terrestrial rocks but common in meteorites.
Native iron combines with chlorophyll to give tree leaves and plants their
green colors but rarely attaches to wood cells.
White is produced by pure silica - SiO2. Since silicon,
Si, and oxygen, O, are the two most abundant elements in the earth's crust.
Silica group minerals are common worldwide. Free silica, SiO2,
referred to scientifically as silicon dioxide, occurs most commonly as quartz.
Quartz is the principal element of glass. In many respects quartz is the most
interesting of all minerals. It has a larger number of distinct varieties with
wider differences than any other mineral. Petrified wood, also referred to as
silicified wood, is a common illustration of a quartz pseudomorph - wood is
slowly replaced, cell by cell, by silica, until not a trace of the original
material remains.
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Process:
The structural arrangement of silicon and oxygen creates an open bonding
structure that permits other ions such as various forms of iron to occupy
interstitial positions in the molecule and bond to it, thus producing
variations in color.
Organic carbon or pyrite - FeS2 (iron sulfide), the most abundant and
widespread sulfide mineral, produces Black. Because it was mistaken for gold it
is often called "fool's gold." Pyrite, translated freely, means
"fire mineral", a reference to the sparks given off when struck.
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Process:
The wood was affected as hydrogen sulfide from decaying organic matter
interacted with iron forming pyrite.
Purple and Blue are produced by manganese dioxide - MnO2.
This is a secondary material formed when water leaches manganese from igneous
rock and re-deposits it as a concentration of manganese dioxide. As a result,
it occurs more often as coatings on other minerals than as large crystals.
Manganese is very important in the manufacture of steel.
Tan indicates silica dioxide is the predominate replacement mineral.
This color is most often seen in permineralized wood. In permineralization, the
wood's cell structure is better preserved, giving it the appearance of real
wood. It should be noted that not all petrified wood is permineralized.
Permineralization also transpires when wood is preserved with calcite rather
than silica.
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How the very fine detail of the cell structure
is preserved is not well understood. It would appear that less than cell sized
gradients in acidity created very small re-precipitation gradients, replacing
the wood on almost an atom by atom basis.
Good Information on the Formation of
petrified Wood:
http://www.geo-logic.org/Minerology/Petrified%20Wood1.htm
http://geology.com/stories/13/petrified-wood/
