The formation mechanisms of Polycrystalline diamonds : diamondites and carbonados

Sammanfattning: Diamond is a cubic carbon mineral that possess many unique characteristics like extreme hardness and thermal conductivity. There are many types of diamonds like monocrystalline, polycrystalline and coated/ fibrous and in this bachelor thesis the focus was on polycrystalline diamonds; carbonado and diamondites (are divided in three different types of diamonds: eclogitic, perioditic -and websteritic-type). I made a literature study on the formation mechanism of diamondites to see whether they have different crystallisation histories than monocrystalline diamonds as some researchers argue. Determing a relationship, or lack thereof, between monocrystalline diamonds and diamondites could be valuable to the mining industry. I also made a literature study on the origin of carbonado because carbonados are important as abrasives in the industries. Constraining an origin for carbonados would give us valuable knowledge about their formation mechanisms, could help us to make synthetic carbonado which could be cheaper than prospecting for natural carbonado. Several origins for carbonado are proposed which are for example meteorite impact, uranium-rich carbonaceous sediments and mantle. The most likely origin is the mantle which is supported among others by textural observations (for example fluid inclusions) but to determine this with certainty a carbon-source needs to be identified in the mantle and komatiite related carbonados. Two different crystallization histories are proposed for diamondites which are; fluids/melts derived from upper mantle or fluids/melts that had a contribution of crustal material. At the moment it is more likely that the formation fluids of E -and P-type diamondites are derived from the upper mantle because there are more evidence that is consistently supported by both eclogitic -and perioditic diamondites. Regarding the websteritic diamondites their formation fluids are more likely to have a crustal origin as all evidence suggest this origin