ASS #3- How Diamonds Form PDF

Ass# 3 : How Diamonds Form What Diamonds Are Made Of: - In 1772, French chemist Antoine-Laurent Lavoisier set a diamond in an oxygen-filled glass jar and used a magnifying glass to direct a concentrated beam of sunlight on it. The diamond down to nothing proving that diamond are made of carbon, Yea...

Ass# 3 : How Diamonds Form What Diamonds Are Made Of: - In 1772, French chemist Antoine-Laurent Lavoisier set a diamond in an oxygen-filled glass jar and used a magnifying glass to direct a concentrated beam of sunlight on it. The diamond down to nothing proving that diamond are made of carbon, Years later, English chemist Smithson Tennant picked up where Lavoisier left off, not until 20 years later the scientific community agree that both finds proved that diamonds were made of carbon Diamonds vs Graphite: - both being made of carbon with being the hardest substance on earth, this is due to the arrangement of atoms that experienced different environments, pressures, and temperatures - Graphite: strong parallel bonds with weak bonds between them - Diamonds: tightly connected strong 3 dimensional bonds in all directions Diamonds and the Earth - Earths Crust: Continental Crust and Oceanic Crust, crust: a layer of hard, strong rock that’s extremely thin compared to the layers beneath it. Its thickness ranges from about 5 to 40 km, though it can be much thicker under mountain ranges,Continental crust is much thicker, more insulating, and generally made up of lighter elements than oceanic crust. Oceanic crust tends to be thin (5 to 7 km), cold, and comprised of much denser elements. - other layer below the crust are: upper mantle, lower mantle, outer core and inner core Mantle: where all diamonds form - The "lithosphere" is the crust and the uppermost part of the mantle, its thicker under mountain ranges and in diamond formation areas,portion of the mantle just under the earth’s crust is rigid and moves with the crust - upper mantle, which extends from about 100 to 410 km beneath the earth's surface, is under greater temperatures and pressures than the lithosphere. - transition zone marks the end of the upper mantle and the beginning of the lower mantle. This zone extends from approximately 410 to 660 km beneath the earth’s surface. - lower mantle is the thickest of the mantle layers and much denser than those above Plate Tectonics - Fifteen plates, both continental and oceanic, make up the surface of the earth. The theory of the formation, structure, and movement of the landmasses is called plate tectonics. - The lithospheric plates are on top of the mobile upper mantle. Mantle convection drives the motion of the plates bringing diamonds closer to the surface - Two plates that move away from one another are called a spreading ridge, where magma (molten rock) from the mobile upper mantle wells up and creates new crust. Subduction: When a continental and an oceanic plate collide, the thinner, colder, denser oceanic plate sinks under the continental plate. This is called subduction - As the oceanic plate is subducted under the continental plate, the basaltic composition of the crust changes to another rock type—eclogite—as it descends into the mantle. - Cratons are the oldest and most geologically stable parts of the earth’s landmasses. Most diamond deposits, still in the rocks that brought them to the surface, are found either on cratons or in the areas surrounding them. - Deepest at the center of cratons, these portions of the mantle are called mantle keels. They can extend down to 250 to 300 km. These depths provide the right temperatures and pressures for diamonds to form Diamond Formation: Source Rocks: - Studies have found that most diamonds form in two types of rocks: peridotite, an igneous rock, and eclogite, a metamorphic rock, both peridolite and eclogite are sources for carbon - Peridotite is an ancient igneous rock that makes up the majority of the rigid lithosphere. - Eclogite is a metamorphic rock that began as basaltic oceanic crust. Heat & Pressure: - they estimated the conditions for natural diamond formation: a temperature range of 900 to 1400°C and pressure between 40 and 80 kilobars. - A kilobar is a unit used to measure extremely high pressure. - Determining where the temperatures and pressures for diamond formation exist required considering the rate of temperature increase with depth in the earth: the geothermal gradient Models: - The majority of diamonds mined are thought to form based on two models: lithospheric and superdeep - Superdeep diamonds form much deeper in the mantle. Some examples of superdeep diamonds include CLIPPIR (Cullinan-like, Large, Inclusion-Poor, Pure, Irregular, and Resorbed), blue, and Juína diamonds. - Diamonds form only in areas where carbon atoms are free to bond with one another without oxygen. - The process of fluids or melts—molten rocks mixed with fluids—reacting with and altering rocks as they pass through them is known as metasomatism. Formation of Super Deep Diamonds: - Superdeep diamonds form much deeper in the mantle, usually in the transition zone (410–660 km) and in the lower mantle (more than 660 km below the surface). - Studies conducted on inclusions in superdeep diamonds indicate that the diamonds formed at this depth. - but superdeep diamond formation is always related to a subducted oceanic plate. CLIPPIR diamonds, blue diamonds, and Brazil’s Juína diamonds are three well-studied examples of superdeep diamonds. - Examples of rare minerals ringwoodite and wadsleyite, and Bridgmanite, calcium perovskite, and majority garnet are also examples of rare minerals that form only deep within the earth.Through high- pressure experiments, scientists know that these much denser minerals can form only in the transition zone or in some meteorites. CLIPPIR Diamonds: - CLIPPIR diamonds (Cullinan-like, Large, Inclusion-Poor, Pure, Irregular, and Resorbed). - “Resorbed” means that the surface of the diamond is partially dissolved during transport and have irregular shapes, - CLIPPIR diamonds are some of the most important in the world because they are large and inclusion-free—and thus rare - metallic melt inclusion are the only CLIPPIR found in this type and is theorized to occur do to the subduction of oceanic plates Blue Diamonds: - Approximately 0.1% of all diamonds mined are blue. The most common cause of blue color in diamonds is trace amounts of boron, the boron in blue diamonds comes from a hydrated oceanic plate (containing seawater) that is subducted into the base of the transition zone and lower mantle, - Inclusions in blue diamonds are rare and consist of minerals that do not exist in the upper mantle or transition zone, Julina Diamonds: - Studies of inclusions in these diamonds have indicated that they formed from carbonate-rich fluids in the mantle transition zone and upper part of the lower mantle Crustal Diamond: - Crustal diamonds form in the crust at or near the earth’s surface. Crustal diamonds are relatively rare, very small, and usually not of gem quality; they are typically used only as abrasives. - One type of crustal diamond is an impact diamond. When a meteorite strikes the earth’s carbon-rich surface, the high pressures and temperatures transform the carbon into diamond. Carbonado Diamond: - Carbonado is an aggregate and the toughest form of diamond. It is used for industrial purposes and is sourced only in Brazil and the Central Republic of Africa - diamond aggregates consist of many tiny randomly oriented intergrown diamond crystals. This structure makes it one of the toughest types of diamond. Diamond Age: -diamonds are pure carbon, they contain no radioactive carbon or other radioactive elements. Therefore they cannot be directly carbon dated or have their ages directly measured by other radioactive decay schemes. -the mineral inclusions in some diamonds have radioactive elements that can be extracted and used to infer the ages of the host diamonds. Garnet and clinopyroxene are two examples. How Diamonds Reach the Surface: - diamonds can only reach the surface if they are transported from the mantle to the earth’s surface. - The deepest hole ever drilled on earth was approximately 12 km deep, much shallower than the 140 km depth and below at which diamonds form. - Diamonds are transported to the earth’s surface in two types of volcanic eruption of igneous rock: kimberlite and lamproite. - Kimberlite is a silica-poor, magnesium-rich rock that contains mainly olivine, and are more common then Lamproite and tend to occur in the middle of cratons - Lamproite is rich in potassium and magnesium; diamond-bearing varieties contain olivine and lack feldspar, and are commonly found at the edges of cratons or immediately around them. - Eruption is a geological process that delivers material to the surface - Diamonds are metastable, meaning they are stable only under the conditions in which they form, - If these conditions change, the carbon atoms within diamond bond differently and become graphite - Kimberlite and lamproite solidify at quite high temperatures because they have very high melting points. - After the hot rock, ash, gases—and possibly diamonds—erupt what remains is a diamond-bearing pipe: a deep vertical formation that results from a kimberlite or lamproite eruption -kimberlite blasts through the continental crust, it produces a deep carrot-shaped formation - lamproite reaches the surface, the explosion is more violent and produces a mushroom shape. - few of these crates have enough diamonds to make it economical to mine