FOSSILIZED OR PETRIFIED WOOD
Prepared by Daniel W. Smith
Chemical Composition: SiO2, Silicon dioxide
Specific Gravity 2.60 to 2.65
Mohs’ Hardness 6.5 to 7.0
Cleavage None
Fracture Uneven to splintery
Color Brown, gray, red, streaks of other colors
Transparency Opaque
Fluorescence None
The fossilization of things that were living is a complicated process. The replacement of organic matter with minerals depends on the chemistry of the environment and the chemical make-up of the once living thing. Fossils are formed by several mechanisms: carbonization, permineralization (petrifaction), replacement, recrystallization, organic traps, and then other processes like the formation of petroleum and coal. These process only happen when the once living things were quickly covered with fine grained sedimentary materials. The outer structure was then preserved in the sediments, then the slow process of replacement of the organic structure occurred.
Carbonization occurs when the mobile oils and other liquids of the organic matter are leached out and the remaining material is reduced to a carbon material. This occurs commonly with plants and rarely with animal soft tissue.
Permineralization occurs when the pores of a once living thing is impregnated by minerals which then crystallize inside the cells. There are three types of permineralization: silicification, pyritization and carbonate mineralization. One of the most common forms is silicification (silica-rich fluids enter the cells. Other minerals such as calcite, silica, and iron can also fill the pores and cavities of the once living thing. Petrifaction occurs when the organic matter is completely replaced by minerals.
Replacement occurs when the once living thing is buried in mud. It’s remains are then replaced by sulfide (pyrite) or phosphate (apatite) minerals. This is a relatively rare process.
Recrystallization is when the existing mineral material undergoes a change such as animal shells (aragonite or calcium carbonate) is changed to calcite. This process destroys the microscopic structure of the original organism.
Organic Traps are where the entire once living thing is trapped and preserved in a material such as asphalt, peat or tree resin.
So called “petrified wood” is a microcrystalline aggregate fossilized by jasper, chalcedony, quartz and to a lesser extent by opal. It is primarily silicon dioxide, valued for its hardness, resistance, durability, colours and wood like patterns that make it so interesting. Fossilzed wood can be found on all the continents.
The most common colours, particularly in Alberta, are brown, gray and red with some green. Other colours commonly found are pink, yellow and blue to violet.
References:
Bauer, J. and Bouska, V. 1983. A Guide in Color to Precious & Semiprecious Stones. Chartwell Books, Inc., New Jersey, pp 152-153.
Schumann, W. 1979. Gemstones of the World. Sterling Publishing Co., Inc., New York, pp 148-149.
Prepared by Daniel W. Smith
Chemical Composition: SiO2, Silicon dioxide
Specific Gravity 2.60 to 2.65
Mohs’ Hardness 6.5 to 7.0
Cleavage None
Fracture Uneven to splintery
Color Brown, gray, red, streaks of other colors
Transparency Opaque
Fluorescence None
The fossilization of things that were living is a complicated process. The replacement of organic matter with minerals depends on the chemistry of the environment and the chemical make-up of the once living thing. Fossils are formed by several mechanisms: carbonization, permineralization (petrifaction), replacement, recrystallization, organic traps, and then other processes like the formation of petroleum and coal. These process only happen when the once living things were quickly covered with fine grained sedimentary materials. The outer structure was then preserved in the sediments, then the slow process of replacement of the organic structure occurred.
Carbonization occurs when the mobile oils and other liquids of the organic matter are leached out and the remaining material is reduced to a carbon material. This occurs commonly with plants and rarely with animal soft tissue.
Permineralization occurs when the pores of a once living thing is impregnated by minerals which then crystallize inside the cells. There are three types of permineralization: silicification, pyritization and carbonate mineralization. One of the most common forms is silicification (silica-rich fluids enter the cells. Other minerals such as calcite, silica, and iron can also fill the pores and cavities of the once living thing. Petrifaction occurs when the organic matter is completely replaced by minerals.
Replacement occurs when the once living thing is buried in mud. It’s remains are then replaced by sulfide (pyrite) or phosphate (apatite) minerals. This is a relatively rare process.
Recrystallization is when the existing mineral material undergoes a change such as animal shells (aragonite or calcium carbonate) is changed to calcite. This process destroys the microscopic structure of the original organism.
Organic Traps are where the entire once living thing is trapped and preserved in a material such as asphalt, peat or tree resin.
So called “petrified wood” is a microcrystalline aggregate fossilized by jasper, chalcedony, quartz and to a lesser extent by opal. It is primarily silicon dioxide, valued for its hardness, resistance, durability, colours and wood like patterns that make it so interesting. Fossilzed wood can be found on all the continents.
The most common colours, particularly in Alberta, are brown, gray and red with some green. Other colours commonly found are pink, yellow and blue to violet.
References:
Bauer, J. and Bouska, V. 1983. A Guide in Color to Precious & Semiprecious Stones. Chartwell Books, Inc., New Jersey, pp 152-153.
Schumann, W. 1979. Gemstones of the World. Sterling Publishing Co., Inc., New York, pp 148-149.