Serpentine Mine, Cyprus, 2007

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Abraham Shawn Bradford
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1 Serpentine Mine, Cyprus, 2007

international ophiolite conference restricted the term ophiolite to only

2 What is an ophiolite? Simply: Ophiolites are pieces of oceanic crust found on land The international ophiolite conference restricted the term ophiolite to only include the following rock types/assemblages This definition has been challenged recently due to recent discoveries made by the IODP

interference colours Pale Green-yellow pleochroism

3 New Mineral you need to know: Serpentine Mg 3 Si 2 O 5 (OH) 4 Fibrous/Fine grained mat like Habit 1 st order interference colours Pale Green-yellow pleochroism Serpentine group of minerals (chrysotile, lizardite, and antigorite)

4 New Mineral you need to know: Talc Mg 3 Si 4 O 10 (OH) 2 Colourless in PPL 2 nd order birefringence Fibrous-bladed habit May be difficult to distinguish from muscovite in thin section easy in hand sample

2H 2 O Green Yellow-pleochroism Bladed-radiating habit *most useful Anomalous blue

5 New Mineral you need to know: Pumpellyite Ca 4 (Mg,Fe 2+ )(Al,Fe 3+ ) 5 O(OH) 3 [Si 2 O 7 ] 2 [SiO 4 ]2.2H 2 O Green Yellow-pleochroism Bladed-radiating habit *most useful Anomalous blue birefringence and yellow-brown birefringence Prehnite Ca 2 Al 2 Si 3 O 12 (OH) commonly associated with pumpellyite NOTE: higher birefringence and more fibrous

6 New texture you need to know: mesh texture Mesh Texture: Hydrothermal alteration produces a network or serpentine interlaced with original igneous minerals

7 Particulars Full rock description of KHAB 2 OR 331/88/1 (worth ½ the lab!) Good Luck!

8 Amphibole

9 Amphibole Anxiety Ortho-amphiboles Vs. Clino-amphiboles

10 Amphibole Anxiety: Ortho-amphiboles There are two common forms of orthoamphibole: Anthophyllite: (Mg,Fe) 2 (Mg,Fe) 5 SiO 22 (OH) 2 Gedrite: (Mg,Fe) 5 Al 2 [Al 2 Si 6 O 22 (OH) 2 ] Orthoamphibole occurs in metamorphic rock of medium-high grade, but not in igneous rocks. Amphiboles are hydrous minerals which break down in anhydrous environments. They are not found in mafic and ultramafic igneous rocks because these magmas have little dissolved water. The amphiboles will break down to form pyroxenes instead. Helpful Hints Orthoamphiboles have parallel extinction Maximum interference colours of first order red and second order blue Brown color of orthoamphibole may be useful in distinguishing it from hornblende, which usually has a green-black color

11 Amphibole Anxiety: Clino-Amphiboles Hornblende (Na,K) 0-1 (Ca,Na,Fe,Mg) 2 (Mg,Fe,Al) 5 (Si,Al) 8 O 22 (OH) 2 Name given to an amphibole with an indeterminate composition Ubiquitous mineral in intermediate igneous rocks and amphibolite facies metamorphism Actinolite Series Ca-rich amphiboles are most common in greenschist-amphibolite facies metamorphism (i.e. meta-carbonates) Tremolite: Ca 2 Mg 5 Si 8 O 22 (OH) 2 White colour in HS; maximum interference colours are upper 1 st order; inclined extinction; large 2V (75-88) Actinolite: Ca 2 (Mg,Fe) 5 Si 8 O 22 (OH) 2 Pale-deep green; negative optic sign Cummingtonite Series Commonly found in mafic metamorphic rocks at intermediate pressures and temperatures Cummingtonite: (Mg,Fe) 7 Si 8 O 22 (OH) 2 Inclined extinction, twins and higher birefringence distinguish from orthoamphiboles; positive optic sign and occurrence distinguish from actinolite series Grunerite: Fe 7 Si 8 O 22 (OH) 2 Subtle pleochroism when compared to cummingtonite Glaucophane series: Na 2 Mg 3 Al 2 Si 8 O 22 (OH) 2 Only found in metamorphic rocks (i.e. Blueschist facies) Distinct pleochroism (colourless-medium blue)

amphibole PART 3 Pyroxene: augite CHAIN SILICATES

amphibole PART 3 Pyroxene: augite CHAIN SILICATES CHAIN SILICATES = INOSILICATES inos = chains Basic structural group: Si 2 O 6 (each tetrahedra shared two corners) Simple or double chains linked by cations