About
The geological specimen that we get or rocks from contains the mineral zircon, which has been age dated at 3.962 billion years. Each and every piece of this rock came from the site where the world’s oldest known intact crustal rock was discovered, on an island in the Acasta River, Nortwest Territories, Canada. Check the area out on google maps.
To make a long story short, when you hold a piece of this rock in your hand you are holding 3,962,000,000 years of history and the oldest know thing on the planet, from the planet.
Discovery
Credit for this find belongs to Dr. Sam Bowring and a team of geologists from the Department of Earth and Planatary Sciences, Washington University of St. Louis. Missouri, the NWT Geological Division of the Department of Northern Development (DIAND) and the Geological Survey of Canada (GSC). This research was also supported by NASA and the U.S. National Science Foundation. The age dating was done by Bowring, I.S. Williams, and W. Compston at the Research school of Earth Sciences, Australian National University, Canberra Australia. The mineral rights to this area wre staked November, 24, 1989 by Yellowknife prospector Walt Humphries and B.E. Weir P.GEOL.
Geology
Without getting into a lot of complex geology and mineralology, the planet Earth is currently thought to be approximately 4.5 billion years old. An early crust formed and a few microscopic fragments dating as far back as 4.1 billion years have been found but never an outcropping. 3.962 billion years ago, part of the crust was metamorphosed into a rock known as Tonalite Gneiss, making it the oldest known rock in the world.
Prior to this particular discovery the oldest known rock was at Isukasia, Greenland, and dated back 3.8 billion years. The oldest known rock in North America, at 3.4 billion years old came from the Minnesota River valley in the U.S.A. The discovery of this rock is an important scientific-geological find and from now on most text books will refer to the 3.962 billion year old Acasta River Gneiss from the Northwest Territories, Canada, as the oldest rock in the world.
What is Gneiss?
This is the generic name of a class of rocks geologically defined as: a coarse grained rock in which bands rich in granular minerals alternate with bands in which schistose minerals predominate.
What is Tonalite?
There are many types of gneiss but the Tonaly Pass in Italy was where the first Quartz-Diorite Gneiss of this type was discovered and described, hence the name Tonalite Gneiss.
Mineral Content
The oldest known rock in the world contains the following minerals:
Zircons (ZrSiO4)
In this case, less than 1% of the rock is composed of micro zircons and these were formed when the rock originally metamorphosed into a Tonalite Gneiss 3.962 billion years ago. They also grew slightly at latter dates of metamorphism (3.6 billion years ago).
Atoms and molecules have a certain size and shape, and like pieces of a jigsaw puzzle, tend to form crystals of a certain shape. As the crystals grow, atoms of uranium are a close enough fit to become locked inside of the crystal, while lead is completely excluded at this stage. However, uranium slowly deteriorates into thorium and thorium slowly deteriorates into lead. By cleaving the zircon crystal and analyzing the ratio of uranium to lead, the age of the rock can be calculated.
Quartz (Sio2)
Is the greyish white mineral.
Plagioclase Feldspars
These vary in composition between NaAlSi3O6 and CaAlSi2O6. These are milky white to orange minerals, often seen in seams. A small amount of red potash feldspar is present in some samples.
Biotite (black mica)
Is the shiny black mineral.
Hornblende
Is the dark (black) mineral.
Alanite, Sphene, Garnet, Magnetite, Pyrite, Chal-copyrite, Sphalerite, and a whole range of trace minerals may be rpresent. This rock was after all formed by the planets primordial geological stew.
To make a long story short, when you hold a piece of this rock in your hand you are holding 3,962,000,000 years of history and the oldest know thing on the planet, from the planet.