Petrogensis of Diamonds in Ureilites (

Topics for Today Explanation of composition of a Ureilite Leading Hypothesis on composition of diamonds. Support for each Hypothesis. Conclusions.

Explanation of Composition of Ureilite Meteorites (25 Samples found) Composed of… – Olivine ((MgFe)SiO 4 ) – Pyroxene ((XY) Z 3 O 6 ) – Pigeonite (Ca.25 (MgFe) 1.75 Si 3 O 6 ) – Graphite (C) – Lonsdaleite (C) – Diamond (C) – Small Percentage of other minerals. (Goodrich et al, 2002)

Explanation of Composition of Ureilite Diamonds range anywhere from 1 m to 9 m Other than diamonds it is the orientation of olivine that exhibits impact impressions (Goodrich et al, 2002)

Explanation of Composition of Ureilite Grouping of the ureilites is based on a schema created by John Berkely et al, (1980) – I: High in FeO/MgO <80 mol% of Forsterite (Mg 2 SiO 4 ) – II: Intermediate in FeO/MgO 80 – 90 mol% of Forsterite – III: Low FeO/MgO <90 mol% Forsterite

Explanation of Composition of Ureilite What separates them from other meteorites 1. Strongly recrystallized 2. Lack minerals created at low temperatures 3. Ureilites pyroxenes are represented by pigeonite. Normally carbonaceous chondrite meteorites contain Orthopyroxene. (Vdovykin, 1963)

Leading Hypothesis Hypothesis #1 – Diamonds resulting in collisions of asteroid bodies. (Vdovykin, 1963) Hypothesis #2 – Composition with in the ureilite parent body. (UPB) (Berkley et al, 1980) Hypothesis #3 – Shock wave pressures from impact. (Goodrich et al, 2002)

Hypothesis #1 Diamonds resulting in collisions of asteroid bodies. (Vdovykin, 1963) – Before falling to Earth asteroids composted of the UPB would collide and these collisions had enough pressure to create the diamonds exhibited by some ureilites.

Vdovykin Asteroid Collisions Support – Small size of diamonds – No craters at impact position – Presence of elongated cavities in urelities Against – Similar circumstances can be caused by shock wave impacts. (discussed later in our talk)

Hypothesis #2 Composition with in the ureilite parent body. (UPB) (Berkley et al, 1980) – Who stated that it was the UPB that created the diamonds. – He is against the idea that it was the shockwaves created the diamonds in ureilites.

Berkley UPB and Diamonds Classification System – I: High in FeO/MgO <80 mol% of Forsterite – II: Intermediate in FeO/MgO 80 – 90 mol% of Forsterite – III: Low FeO/MgO <90 mol% Forsterite (Berkley et al, 1980)

Berkley UPB and Diamonds (Based off information from Berkley et al, 1980)

Hypothesis #3 Shock wave pressures from impact. (Goodrich et al, 2002) – The commonly accepted idea that it was shockwave pressures that is created when a meteorite hits the earth that causes the diamonds to be formed.

Goodrich Shockwave Pressure Slightly in conflict with Vdovykin and his idea of asteroid collisions. Slightly different he has evidence that supports his ideas with new evidence. This evidence is that those with out diamonds exhibit low shock levels. Opposed to those who have diamonds have high shock evidence. (Goodrich et al, 2002)

Goodrich Shockwave Pressure This was done through the analysis of of olivine and graphite. – Olives did not have and undularated extinction – Shock lamellae in graphite. (Goodrich et al, 2002)

Conclusions Three Hypothesis – Asteroid collision model (Vdovykin, 1963) – Composition with in the ureilite parent body. (UPB) (Berkley et al, 1980) – Shock wave pressures from impact. (Goodrich et al, 2002)

Conclusions Who’s Correct? – All could be all could not be, no definitive answer to the question… – Where do ureilites?

Thank You Dr. Bernhard Saini-Eidukat Dr. Allan Ashworth

Thank You