Clinopyroxene. Pyroxene. Clinopyroxene. Compositional Groups

Transcription

1 Cpx - or Cli Monolini Composition sed on 3 end memer omponents CSiO 3 - wollstonite MgSiO 3 - linoensttite FeSiO 3 - linoferrosilite Cpx generl formul Augite C,Mg,Fe,Al) 2 (Si, Al) 2 O 6 Common px hedenergite CFeSi 2 O 6 diopside CMgSi 2 O 6 Vrile omposition = vrile optil properties Compositionl Groups Pyroxene Refrtive Index n α = n β = n γ = Generlly the higher Fe ontent the higher the RI Will exhiit moderte to high relief, with medium irefringene 2 nd order lue to yellow interferene olours ixil +ve, with 2V Z = 25-70, inreses with inresing C. 1

2 OAP All linopyroxenes rystllize with the sme struture nd there is omplete solid solution mong ll speies nd they nnot e distinguished relily sed on their optil properties When identifying linopyroxene it is est to ll it li linopyroxene. To identify speifi linopyroxenes requires more dvned tehniques Monolini 3 rystllogrphi xes, unequl length, not mutully perpendiulr ^ = 105 The rystllogrphi nd inditrix xes do not oinide X^ = -20 to -33 (X lies in ute ngle etween & ) Y = Z^ = +35 to 48 (Z lies in otuse ngle etween & ) OA Z OA X Y Colour nd Pleohroism Cpx grins re usully olourless, ut my e grey, ple green, rown or rownish-green. Drker pleohroi olours my reflet more iron rih ompositions X = ple green, luish-green Y = ple greenish-rown Z = ple rownish-green, green, yellow-green Titnugite (Ti-rih ugite) displys muh more distintive rown-violet pleohroism (resemles opx). 2

3 OAP Clevge, Frture typil pyroxene levges prllel to {}, whih interset t ~90 Bsl setions showing two levges nd exhiit symmetril extintion. Longitudinl setions, ut prllel to (), show prllel extintion nd re length slow. Longitudinl setions, ut prllel to (), show mximum irefringene, exhiit one levge nd hve inlined extintion with Z^ = +35 to 48. Form euhedrl rystls, stuy prisms, four or eight-sided (sl setions) with 2 levges longitudinl setions re retngulr nd exhiit one levge; my form euhedrl grins, irregulr msses tht enlose ssoited minerls z to xis X Z' Y Setion of Symmetril Extintion Off Centred Opti Axis or BxFigure Opti Plne ll to 3

4 OAP z to xis OA Z OA X^ = X Z^ = V X = Setion of ll to Inlined extintion Opti Norml Figure Mximum Interferene Colour z to xis Z X' Y Setion of Prllel Extintion Off Centred Bxo Altertion ommonly lters to urlite ( fg, light oloured mphiole), or my lter to serpentine, hlorite, iotite, rontes nd /or other silites Ourrene ommon in mfi igneous roks, lkli-rih vrieties my e found in more silii roks, often ssoited with olivine, orthopyroxene, nd plgiolse 4

5 Distinguished from opx y: 1. inlined extintion 2. higher irefringene, higher interferene olour 3. lower 2V ngle 4. opti sign (+ve) 5. Often opx nd px re found together in the sme rok, olivine my lso e present pge X^ = , Y=, Z^= Linking rystllogrphi nd opti fetures in If the lotion of Y n e identified then : 1) the position of the OAP (XZ plne) n e determined, nd 2) The lotion of n e determined How to determine the position of the OAP X^ = , Y=, Z^= Linking rystllogrphi nd opti fetures in At Extintion Virtion diretions re prllel to rosshirs 45 from Extintion Upon inserting the Gypsum Plte Colours n either derese or Colours n inrese, prllel to plte 5

6 Y X^ = , Y=, Z^= Linking rystllogrphi nd opti fetures in Slow Ry OAP = Y Z X Fst Ry Fst Ry = X Slow Ry At Extintion Working kwrds to the grin t extintion 45 from Extintion Upon inserting the Gypsum Plte If olours derese then Y is 90 to plte X^ = , Y=, Z^= Linking rystllogrphi nd opti fetures in If the lotion of Y n e identified then : 1) the position of the OAP (XZ plne) n e determined, nd 2) The lotion of n e determined Alterntively n look t the Interferene Figure, Whih for this orienttion will e n off entred Bx or n off entred Opti Axis Figure Off Centred Bx or OA X^ = , Y=, Z^= Linking rystllogrphi nd opti fetures in OAP Bx M OAP M n β Bx n Bxo At Extintion 45 from Extintion Need to determine whether the n Bxo = Fst (n α ) or Slow (n γ ) ry? 6

7 Off Centred Bx or OA X^ = , Y=, Z^= Linking rystllogrphi nd opti fetures in Y X OAP OAP n β Z n Bxo = n α n β Bx n Bxo M n Bxo = n α 45 from Extintion nd remove Bertrnd lens 45 from Extintion Upon inserting the Gypsum Plte If olours derese then n Bxo = n α X^ = , Y=, Z^= Setion of z to xis Determining the position of the inditrix xes in n OAP Setion Find grin tht exhiits: The highest interferene olour A single levge prllel to the length Align the levge with the rosshir, ross the polrs. The grin will not e t extintion X^ = , Y=, Z^= Setion of z to xis Rotte the grin to extintion X or Z EA X or Z 7

8 X^ = , Y=, Z^= Setion of z to xis Rotte the grin 45 X or Z EA X or Z Determine whether the ry virting NE-SW is the Fst or Slow ry X^ = , Y=, Z^= Setion of z to xis Fst Ry = X Slow Ry = Z Insert the Gypsum Plte nd test whether the ry virting prllel to the plte is the fst or slow ry If the olours inrese, the slow ry is prllel to plte If the olours derese, the fst ry is prllel to the plte Z = Slow Ry Z^ X = Fst Ry X^ = , Y=, Z^= Setion of z to xis Rotte the grin to strting position Hve determined: The position of the inditrix xes (X nd Z) in this grin The extintion ngle (Z^) for this grin If the grin were pleohroi, the olours ssoited with X nd Z The mximum irefringene Highest Interferene Colour 8