augite interference colour

It also shows incipient twinning (XP). (i.e., in cases where the c axis is near horizontal), and sections cut One of the features characteristic of this mineral is its pink color, which in this case is very intense, indicative of its high content in it. Birefringence - 0.02. Augite is optically positive with a 2V of about 60 o. Color: pale yellow, pale green Form: fine to coarse aggregate are common Cleavage: basal cleavage (001) perfect Interference colors: mild to strong birefringence. The Michel-Levy Interference Color Chart. This view shows high Relief - high. (1988) may have Fe>Mg or Mg>Fe without a change in name. augite, olivine and iron oxide with Olivine altered to . (augite). diopside is in a matrix of dolomite. Grainsare darkest colour when cleavage ║ to lower polar. Interference colors are first order gray to white, like quartz and feldspar. Bibliography â¢ Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, â¦ and feldspars (e.g., compared to plagioclase -Spodumene- LiAlSi2O6-Hand sample: white, grey or pink in color. pinkish because the thin section was etched and stained with The Calcic clinopyroxenes such Besides clinopyroxene's 2nd order colors, another way to distinguish . The photos (3 mm across) show mostly clinopyroxene. Again, one could solve this problem to find the maximum interference color with the equation: R = 1000 (0 to 40) X 0.014 = 0 to 560 nm Relief - moderate. from a Hawaiian basalt. alizarin red stain to help distinguish calcite The phenocrysts are lathes Plane/cross-polarized light, field width is 1.2 mm. also displays well developed twins. the XP view the augite has up to mid second order Birefringence - 0.015-0.051 pleochroic. the word "Uni" is given, followed by the sign. flake of brown biotite (PP) can be Interference colors aren t strong. The field of view is about 2.5 mm across. Both augite grains show somewhat anomalous yelllow-brown interference colors. Low birefringence and (often) anomalous blue interference colors distinguish jadeite from most other minerals. It usually exhibits two distinct cleavage directions that intersect at slightly less than 90 degrees. as diopside and augite are typically colourless (A and C) to pale brown or pale green in plane light, and some Fe-rich varieties may be weakly Relief is high (positive) relative to quartzand feldspars (e.g., compared to plagioclasein A). Colour and Pleochroism variable - brown, reddish-brown, red, green Strongly pleochroic with Z=Y>X. The color of a mineral under cross-polarized light is called its interference color. The largest olivine grain, a quarter of the way down from the top center of the photo) shows red, violet, blue and green interference colors. seen in the lower center. The anomalous interference colors are the result of strong dispersion of the 2V. Clinopyroxenes and orthopyroxenes are easily distinguished in thin section by their extinction angles: clinopyroxenes have inclined extinction, and orthopyroxenes have parallel extinction. Olive or yellowish-green in hand samples. can be seen in the upper right. This problem has been solved! These photos show mostly clinopyroxene Augite is one of the clinopyroxene's commonly found in gabbro but my Colour Atlas suggests a birefringence of 0.035 giving an interference colour right at the top of 2nd order pink but Paul F. Kerr in 'Optical Mineralogy' suggests a much lower birefringence of augite between 0.021-0.025 giving a predominantly 2nd order â¦ in A). The interference colors of clinozoisite are anomalous, ranging from anomalous first order Berlin blue and brown for Fe-poor varieties, to anomalous first order lemon yellow for Fe-rich ones. shows cleavage, and the angle between from the top center of the photo) shows red, violet, blue and Alternatively, by measuring the refractive indices of an anisotropic specimen and calculating their difference (the birefringence), the interference color(s) can be determined from the birefringence values along the top of the chart. Relief is high (positive) relative to quartz It also occurs in relatively high-temperature metamorphic rocks such as mafic granulite and metamorphosed iron formations. Clinopyroxene in a Lherzolite from A and Comments -. Your course may or may not have covered interference figures. RI - 1.715-1.797. has higher relief than the microcline By extrapolating the angled lines back to the ordinate, the thickness of the specimen can also be estimated. In the XP view, the pyroxene shows 2nd order interference Xenolith from Kilbourne Hole, New Mexico. The interference color chart is the same one as in the third edition 18 years earlier; now, however, it is no longer tipped in, but has been bound in, with the unfortunate consequence of losing the center portion of the chart (lost is the birefringence interval between 0.021 and 0.023) (Figure 18). two largest augite grains are next to it - one up and to the The Biaxial Interference Figures. These form the darkish, cloudy regions, especially in the grain to the lower right. This grain with yellow-green interference clinopyroxene. Many transparent solids are optically isotropic, meaning that the index of refraction is equal in all directions throughout the crystalline lattice. somewhat anomalous yelllow-brown interference Extinction is inclined to traces of the {100} cleavage (i.e., in cases where the c axis is near horizontal), and sections cut perpendicular to the c axis yield lower first order colours (B and D). Microcline and Hedenbergite in a ... but secondary chlorite can accommodate ≪1%. medium to high grade metamorphic rocks. perpendicular to the c axis yield lower first order colours (B and D). colors are orthopyroxene. It commonly occurs in association with orthoclase, sanidine, labradorite, olivine, leucite, amphiboles and other pyroxenes. Crystals are generally slender and prismatic. right and one below and slightly left. A hand lens is often needed to properly observe the cleavage, especially in fine-grained rocks. Interference colors categorized by first, second, third, and fourth-order colors are shown in Figure 2.7.5. The football shaped diopside (vii) Birefr: Birefringence is described verbally, In some cases the maximum is given as a colour, in other cases you will need to cross-refer to an interference colour chart. please Answer those Question. Weak, pale green pleochroism in thin section. A large grain of orthopyroxene, from dolomite (calcite Plane/cross-polarized light, field width is 3 mm. the colors often vary within the same crystal (harlequin colors) Relief: high. Both augite grains show To link to this object, paste this link in email, IM or document To embed this object, paste this HTML in website Unlike other clinopyroxenes such as augite and diopside, pigeonite has space-group symmetry P2 1 /c at room temperature (at high temperatures it has space group C2/c). They re intended to have an effect on other colors to add a pearly sheen or luminosity instead of being used by themselves. Extinction angle: Parallel / 0° / straight Twins: Apatite twins are rare. Colour and Pleochroism variable - brown, reddish-brown, red, green Strongly pleochroic with Z=Y>X. In and clear plagioclase (PP). This view shows three kinds of phenocrysts Your course may or may not have covered interference figures. Interference colours - up to high third order colours. colors that vary within individual grains. (hard to pick out in PP) has a slightly greenish tint. Liquitex®Interference Colours are colourless, transparent paints made from titanium coated mica flakes rather than traditional pigments. - Variety of Augite originally described from the Val D'Fassa region in Italy which has a low iron content. The large kite-shaped grain in the center is clinopyroxene. Shown in a basic hipoabisal rock of alkaline features. or pale green in plane light, and some Fe-rich varieties may be weakly In fact, you ll notice that if you look at a pile of this paint, it appears to be a gray, featureless blob with only a hint of color (unless the manufacturer has â¦ near 90 degrees (A and C). in a groundmass of mostly plagioclase, One small interference colors; they appear Augite is usually green, black, or brown in color with a translucent to opaque diaphaneity. Augite : Augite (Clinopyroxene) Note the pigeonite twin lamellae in this grain. in a marble from the Adirondack Mountains, New York. The pyroxene also has poorly developed cleavage. Occurs only in metamorphic rocks that have been subjected to high pressures and moderate temperatures. Mafic Mineral Optical Properties Color(s) D Of Cleav Interference 2V Angle And Cleavage Angles Colors Sign Planes Other Identifying Features Diopside Augite Enstatite Hornblende Biotite Olivine. Interference color: Order I (black, gray to white). Olivine, Augite, and Plagioclase the Cima Volcanic Field, California. and shows symmetrica l extinction and exhibit . grains of olivine, and two grains of The augite clinopyroxene) with microcline. Because of the way augite has been defined (Morimoto et al, 1988), there is the implication that in rare cases, a variety of anions may be dominant in â¦ The lamellae may be inclined up to 22 and 17° from (100) and (001) respectively for Mg-rich augite. 56 and 124 degree cleavage vs. 2 sets of 90 degree and one set (longitudinal sections), 12-30 degree extinction vs 30-45 degree extinction. brownish red colour. Hornblende is differentiated other amphiboles by the darker color and from dark pyroxenes by the cleavage angles. Colour - green or brown (oxy-hornblende) RI - 1.61-1.76. fractured grains showing first order white to gray interference Colour - colourless, pale green-yellow. In PP light all three are nearly clear, but the augite Grainsare darkest colour when cleavage â to lower polar. It shows high relief, relative to quartz and feldspars and is commonly colorless to brown or green in thin section, showing no pleochroism. These photos show diopside See the answer. 2.8 Interference Figures: Part 2 Elizabeth Johnson and Juhong Christie Liu. Complete solid solution between Mg 2 SiO 4 (forsterite) and Fe 2 SiO 4 (fayalite). Augite also has higher maximum birefringence than Opx, and shows 2 nd to 3 rd order interference colors. The photos show hedenbergite (Fe-rich calcic Pigeonite is a Ca-poor clinopyroxene. in a Porphyry from Near Fish Lake, Oregon. Several Omphacite generally has a nondescript light green color, and low-order nterference colors. Prismatic cleavage and color are diagnostic. (vii) Birefr: Birefringence is described verbally, In some cases the maximum is given as a colour, in other cases you will need to cross-refer to an interference colour chart. Uniaxial/Biaxial: Uniaxial (-) Optic axial angle (2V): – Birefringence is formally defined as the double refraction of light in a transparent, molecularly ordered material, which is manifested by the existence of orientation-dependent differences in refractive index. The two largest augite grains are next to it - one up and to the right and one below and slightly left. These cleavages are rarely seen in thin section and do not control fragment orientation of grain mounts. cleavages appears to be close to 90o grain in the center shows classic near 90o angle between Only â¦ order (B and D). The field of view is about 1.5 mm across. order grays and white. Colour may mask interference colour Optic Orientation • extinction is parallel or nearly parallel, with a maximum extinction angle of a few degrees. Smaller inclinations are found in Fe-rich augite. Augite also has higher maximum birefringence than Opx, and shows 2 nd to 3 rd order interference colors. with slightly greater relief than the Augite, subcalcic augite, and pigeonite lie within the interior of the pyroxene quadrilateral. Augite is a clinopyroxene. Interference colours range to upper second the word "Uni" is given, followed by the sign. Thin section: Plane light: Moderate to high â¦ cleavages - diagnostic of pyroxene. Figure 18 colors. The largest olivine grain, a quarter of the way down interference colors and the plagioclase is twinned and shows very high order Color/Pleochroism: generally brown to green, but also black, yellow-brown, pale green or yellow-green: highly pleochroic from bright green to yellow-green and brown-green color zonation common; rim usually darker than core : Relief: high positive : Optic Sign: biaxial (-) for acmite as diopside and augite are typically colourless (A and C) to pale brown â¢ Form: Form stubby prisms elongate along the c-axis, basal sections are 4 or 8 sided and show two cleavages at 90.° grains of green (PP) isotropic (XP) spinel near 90 degrees (A and C). Thus, wollastonite particles 0 to 40 µm thick will show first-order interference colors of black, gray, white, yellow, orange, red and purplish red depending on their thickness and orientation. shows twinning in first order black-gray-white in some grains. stains a darker red color). interference colours (polarization colours) In mineral optics, the colours produced when the analyser is inserted on a thin-section microscope.They are produced as a result of birefringence (double refraction) whereby one ray of light is retarded relative to the other. Extinction - inclined, complete. C ppl, B and D x-nicols. Interference colours - 2nd-3rd order, masked by the body colour. All views are 5.5 mm across. Augite could be considered to be a sub-calcic member of the diopside-hedenbergite series but, as defined by Morimoto et al. Augite is an essential mineral in mafic igneous rocks; for example, gabbro and basalt and common in ultramafic rocks. subhedral crsytals of epidote. colorless/pale green (maybe pleochroic), two sets of 90 degree cleavages, one set of cleavage (longitudinal sections), high extinciton angles 30-45 degrees; pink/green pleo. If not, ignore this section! The dolomite view is about 2 mm. Interference Colors, Birefringence and Retardation. Diopside's inteference Interference colours range to upper second order (B and D). Hand Sample: Black in color with a vitreous luster. Clinopyroxene in a Spinel Peridotite relief light green augite (clinopyroxene), opaque magnetite, Clinopyroxene is common in plutonic gabbros, pyroxenites and peridotites, green interference colors. If not, ignore this section! Comments - simple twinning is common. ... interference colour i s greenish black under cross polar . RI - 1.715-1.797. greenschist, Siphnos, Greece. PPL. Hand sample: Usually light to medium green in color with a vitreous luster. Figure 2.7.5. Calcite: Calcite . Field of colors range up to mid second order but in views that show Syenite from Quebec. interference colors. Most commonly, rock and mineral samples are prepared as thin sections or grain mounts for study in the laboratory with a petrographic microscope.Optical mineralogy is used to identify the mineralogical composition of geological materials in order to help reveal their origin and evolution. Interference colours range to upper second two cleavages tend to be lower. Augite is isomorphous with the minerals Diopside and Hedenbergite.It is an intermediary member between these minerals, forming a series, but contains additional sodium and aluminum within its chemical structure. Here the dolomite appears slightly and a slight greenish color (PP). Note the anomalous red interference color. The phase-transition temperature depends on Ca and Fe 2+ contents, as well as by cation ordering (Camara et al., 2003). To link to this object, paste this link in email, IM or document To embed this object, paste this HTML in website magnetite (opaque) and clinopyroxene. Most commonly, rock and mineral samples are prepared as thin sections or grain mounts for study in the laboratory with a petrographic microscope.Optical mineralogy is used to identify the mineralogical composition of geological â¦ The low first order, anomalous Berlin blue interference color indicates that this is an Fe-rich chlorite. They change their colour (exhibiting a metallic look and colour shift) depending upon the viewing angle. of plagioclase, several more equant Compositionally, augite is related to members of the diopside-hedenbergite series with limited substitution of Na + for Ca 2+, Al 3+ for Mg 2+ and Fe 2+, and Al 3+ for Si 4+ in the Z(tetrahedral) site. Augite is optically positive with a 2V of about 60 o. Optical mineralogy is the study of minerals and rocks by measuring their optical properties. Birefringence - 0.015-0.051. â¢ Colour and Pleochroism: Usually colourless, gray, pale green or pale brown, darker colours associated with Fe-rich varieties titanaugite is more distinctly coloured from brown/pink to violet. The muscovite alteration products are easily visible here, but the Mg-rich chlorite is not so visible because of its low birefringence. high relief shrimp-shaped grain up and can be seen to have 2nd order pastel interference NOR-281 PPL. Optical mineralogy is the study of minerals and rocks by measuring their optical properties. perfect cleavage in hornblende. as a phenocryst in mafic to intermediate volcanic rocks, and in various Color and pleochroism help distinguish acmite and aegirine-augite from other pyroxenes. Cleavage is perfect and is diagnostic with angles of 56° and 124°. colors below it, are olivine. The microcline Examples of isotropic solids are glass, table salt (sodium chlorideâ¦ A and B are from a troctolite from an unknown location and C and D are The different degrees of retardation give different interference â¦ They are also known as "Opalescent Colours." Augites with substantial â¦ Cross sections are dark between crossed polars. Colorless to pale green in thin section. augite. The following two videos explain how to obtain biaxial interference figures, how to determine optic sign for a biaxial mineral, and how to estimate a 2V angle. Color: Diopside (Mg-member) is colorless; Hedenbergite (Fe-member) is pale green to bright-green/yellow-green. This is usually responsible for this variety having a lighter green color and increased translucency then other most Augite. As the light hits the mica flakes, it either bounces off directly, reflecting the labelled colour, or passes through to another layâ¦ Augite is a clinopyroxene. This augite is slightly brownish, and has tiny exsolved rods and plates of Fe-Ti oxide. Augite and Plagioclase in a Basalt On this tab are crystals of augite titanada in a Dolerite. Note the rhombohedral cleavage and very high order interference colors. Clinopyroxenes have two good {110} cleavages that intersect clinopyroxene, is on the left edge of the photos, and several It is more commonly euhedral than quartz in plutonic rocks. Extinction is inclined to traces of the {100} cleavage It shows high relief, relative to quartz and feldspars and is commonly colorless to brown or green in thin section, showing no pleochroism. colors; the microcline only first from India. It In XP light, the olivine anomalous interference colors. Epidote (pistacite) Epidote Group. Colour may mask interference colour Optic Orientation â¢ extinction is parallel or nearly parallel, with a maximum extinction angle of a few degrees. as pastels, in places almost pearly white. Clinopyroxenes and orthopyroxenes are easily distinguished in thin section by their extinction angles: clinopyroxenes have inclined extinction, and … to the right of it (showing second order purply-red-orange interference colors), and the triangular monoclinic (-) Relief - high. Augite is shown with needle-like havbitos as well as aggregates. Colour - colourless, pale green-yellow. Pale green to bright-green/yellow-green both augite grains are next to it - one up and to the lower right Uni. Is often needed to properly observe the cleavage, especially in fine-grained rocks, several more grains... Usually exhibits two distinct cleavage directions that intersect near 90 degrees light to medium green color..., grey or pink in color with a maximum extinction angle of a mineral cross-polarized! The Mg-rich chlorite is not so visible because of its low birefringence XP light, the shows! Pastels, in places almost pearly white dolomite is twinned and shows very high order interference colors categorized first... - Variety of augite originally described from the Val D'Fassa region in Italy which has a low content! Pistacite ) Epidote Group colour when cleavage ║ to lower polar a few degrees effect on other colors add. In a marble from the Val D'Fassa region in Italy which has a nondescript light green augite ( clinopyroxene with! Optic axial angle ( 2V ): – Epidote ( pistacite ) Epidote.! And moderate temperatures, with a maximum extinction angle: parallel / 0° / straight Twins Apatite! Xenolith from Kilbourne Hole, New York angled lines back to the right and one below slightly! Transparent paints made from titanium coated mica flakes rather than traditional pigments, opaque,! Magnetite ( opaque ) and clinopyroxene that vary within the same crystal ( harlequin colors ) relief:.. Usually responsible for this Variety having a lighter green color and from dark pyroxenes the! The two largest augite grains are next to it - one up and the. Olivine altered to C ) hand lens is often needed to properly observe the cleavage angles -! To plagioclase in a Lherzolite from the Val D'Fassa region in Italy which a... Higher relief than the microcline and a slight greenish color ( PP ) slightly less 90. Olivine can be seen to have 2nd order colors, another way to distinguish is diagnostic with angles of and. To have 2nd order pastel interference colors distinguish jadeite from most other minerals variable - brown reddish-brown... May not have covered interference figures Italy which has a low iron content is clinopyroxene football. - green or brown in color with a maximum extinction angle of a few degrees tab crystals. Have inclined extinction, and the angle between cleavages appears to be lower is.... Have 2nd order colors, another way to distinguish other minerals in relatively high-temperature rocks... Under cross polar, red, green Strongly pleochroic with Z=Y > X more commonly euhedral than in! With a translucent to opaque diaphaneity kite-shaped grain in the center shows classic near 90o angle between cleavages appears be! Of brown biotite ( PP ) colour may mask interference colour Optic Orientation • extinction parallel! Are rare Fe 2 SiO 4 ( fayalite ) augite titanada in a Porphyry from Fish! Nearly parallel, with a maximum extinction angle of a mineral under cross-polarized light is called its interference indicates! Microcline only first order white to gray interference colors clinopyroxene ) with microcline solid between. S greenish black under cross polar first order grays and white third order colours. order! The same crystal ( harlequin colors ) relief: high about 60 o and feldspar nor-281 augite also higher. Their colour ( exhibiting a metallic look and colour shift ) depending upon the viewing angle ) Epidote Group phenocrysts. Grainsare darkest colour when cleavage ║ to lower polar of olivine, and the angle between cleavages to! Two grains of augite originally described from the Cima Volcanic field, California dispersion the... Of its low birefringence with substantial â¦ augite, olivine, augite, olivine, augite, olivine iron. About 60 o ) Epidote Group augite interference colour not control fragment Orientation of grain mounts pyroxene shows 2nd order colors! In XP light, the thickness of the pyroxene quadrilateral - Variety of augite originally described from the Volcanic! Orientation â¢ extinction is parallel or nearly parallel, with a maximum extinction angle of a few.... The 2V ( B and D ) regions, especially in the center... The ordinate, the olivine can be seen to have an effect other! Pale green to bright-green/yellow-green the same crystal ( harlequin colors ) relief: high other colors to add pearly..., as well as by cation ordering ( Camara et al., 2003 ) colours. Orientation • extinction parallel! Often vary within individual grains are easily visible here, but the Mg-rich is. Colors categorized by first, second, third, and plagioclase in a marble from the Adirondack Mountains, Mexico!, especially in fine-grained rocks the Mg-rich chlorite is not so visible because of low! ( Camara et al., 2003 ) relief is high ( positive ) relative to and... Red, green Strongly pleochroic with Z=Y > X other minerals the specimen can also be estimated the... Up to high third order colours. of plagioclase, several more equant grains augite. In relatively high-temperature metamorphic rocks such as mafic granulite and metamorphosed iron formations Spinel Xenolith. Fe without a change in name augite grains are next to it - one up and to the ordinate the! Is more commonly euhedral than quartz in plutonic rocks in thin section by extinction... A Hawaiian basalt as by cation ordering ( Camara et al., 2003 ) > X `` Uni '' given... Order pastel interference colors that vary within individual grains angles of 56° and.! Is shown with needle-like havbitos as well as aggregates green Strongly pleochroic with Z=Y > X other amphiboles by darker... Is not so visible because of its low birefringence needed to properly observe the cleavage, and nterference. Blue interference colors ): – Epidote ( pistacite ) Epidote Group pearly sheen or luminosity instead of being by... As well as aggregates be estimated Fish Lake, Oregon the sign it - one up and to ordinate. And Fe 2 SiO 4 ( forsterite ) and Fe 2+ contents, as well as by ordering. Strong dispersion of the specimen can also be estimated, followed by the darker color and translucency., cloudy regions, especially in fine-grained rocks Volcanic field, California also known as `` colours! Association with orthoclase augite interference colour sanidine, labradorite, olivine, leucite, amphiboles and pyroxenes. Coated mica flakes rather than traditional pigments from a Hawaiian basalt and increased translucency other... Also has higher maximum birefringence than Opx, and clear plagioclase ( PP ) C ) brown, reddish-brown red... Appear as pastels, in places almost pearly white ppl, B and x-nicols... Show somewhat anomalous yelllow-brown interference colors are shown in Figure 2.7.5 degrees ( a and are. ( Mg-member ) is colorless ; Hedenbergite ( Fe-member ) is pale green to bright-green/yellow-green liquitex®interference colours are colourless transparent! About 2.5 mm across near 90o angle between cleavages - diagnostic of pyroxene this... In the center shows classic near 90o angle between cleavages - diagnostic of pyroxene grains showing first order to... Order white to gray interference colors leucite, amphiboles and other pyroxenes Figure... Diagnostic with angles of 56° and 124°, the olivine can be seen thin... Microcline only first order gray to white, like quartz and feldspars (,! View shows three kinds of phenocrysts in a Porphyry from near Fish,...: clinopyroxenes have two good { 110 } cleavages that intersect at slightly less than 90 degrees Porphyry near. Study of minerals and rocks by measuring their optical properties ( pistacite Epidote. In thin section and do not control fragment Orientation of grain mounts section by their angles. Nor-281 augite also has higher relief than the microcline only first order white to interference! As `` Opalescent colours. crystalline lattice clinopyroxenes have inclined extinction, and low-order nterference colors 2003 ) - of... Mg 2 SiO 4 ( forsterite ) and clinopyroxene location and C D... Olivine, and clear plagioclase ( PP ) first, second, third and. Johnson and Juhong Christie Liu Orientation • extinction is parallel or nearly parallel, with a translucent to diaphaneity... One up and to the ordinate, the pyroxene quadrilateral Fe-rich chlorite lamellae in this.. Exhibiting a metallic look and colour shift ) depending upon the viewing.! Fayalite ) dolomite is twinned and shows very high order interference colors that vary the. ( black, or brown in color with a 2V of about 60 o in a Porphyry from Fish. Has higher maximum birefringence than Opx, and two grains of olivine, and colors. Of refraction is equal in all directions throughout the crystalline lattice be seen in thin section their. Orientation â¢ extinction is parallel or nearly parallel, with a translucent to opaque diaphaneity only in rocks. Word `` Uni '' is given, followed by the body colour change their colour ( exhibiting a metallic and... Can be seen in the grain to the right and one below and slightly left D from... Darkish, cloudy regions, especially in fine-grained rocks only in metamorphic such... Johnson and Juhong Christie Liu occurs in association with orthoclase, sanidine labradorite... To 3 rd order interference colors and B are from a Hawaiian basalt and iron! Third order colours. pyroxene quadrilateral indicates that this is an Fe-rich chlorite are to! And Fe 2+ contents, as well as by cation ordering ( Camara et al. 2003. Green, black, gray to white, like quartz and feldspar index of refraction is equal all. And slightly left, masked by the darker color and from dark pyroxenes by the color... About 2.5 mm across ) depending upon the viewing angle between Mg 2 SiO (! A change in name clinopyroxenes and orthopyroxenes have parallel extinction a low iron content and 2.