SYENITE, IJOLITE, CARBONATITE, ULTRAMAFIC ROCKS AND LAMPROPHYRE

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1 SYENITE, IJOLITE, CARBONATITE, ULTRAMAFIC ROCKS AND LAMPROPHYRE #13 Hornblende subh mm laths 3% gray mm 53-58% -subh White mm laths mm 14% -euh mm equant,, or polyhedral The K-spar is probably orthoclase, and is very difficult to distinguish from plagioclase. sphene - amber, grains,. #14 Alkali 10% Subh 0.5 mm laths 80% White/gray 0-4% -subh mm Show some lineation/foliat ion. 0-4% -subh mm Show some lineation/folia tion. Granitoid. SPHENE - 1%, amber, anh, <0.5 mm. Pyrite, as a thin surface coating. Amphibole/pyroxene difficult to distinguish. #17 Nepheline 2% Subh laths 63-83% Pink 5-20% -subh mm Granitoid. NEPHELINE , anh, hazy,, rounded. 1

2 #18 Nepheline-Sodalite 18-24% White/gray mm 36-47% Pink/white mm 2-8% 2 mm 7-20% mm Elongated SODALITE %, anh-subh, blue-gray, mm, equant. LW-UV: bright orange. NEPHELINE - 5-8%, anh, hazy, 6 2 mm, rounded. #20 Siderite Carbonatite 10% Thin bands Medium grained. Layered. CARBONATE - 60%, anh, white to weathered brown, 2 mm, thin bands. SIDERITE - 20%, anh, brown to reddish, < 0.5 mm. PYRITE - Cubic, 2%,. LIMONITE - surface coating, yellow, powdery. RARE EARTH CARBONATE or CHLORITE - 3% surface coating, lumpy, blue-green, scattered blotches. #328 (Arkansas) mm Few scattered crystals -sbh mm NEPHELINE - weathered, about 1 2

3 #329 (Colorado) (see K-spar) 50% (with plagioclase) -sbh Pink (partly due to surface weathering - makes identification of K-spar/ Plagioclase impossible mm 20% -sbh equant to NEPHELINE - 2, anh, hazy, 1 mm, surrounds the amphibole. Plagioclase Nepheline K-Spar Biotite Hornblende #19 Ijolite 40% White to hazy 15-20% 40-4 Variable shape Some show Schiller luster, indicating orthopyroxene. Medium grained. 3

4 APHANETIC TO Plagioclase Olivine Biotite Hornblende Ortho- Chromite #39 Lamprophyre 5-7% Whitish gray (may be partially Nepheline) 85-90% Dark green Dull, translucent in places, rounded. 5-8% (May be pyroxene) Aphanitic to fine-grained. WEATHERING PRODUCTS: Orangish Hematite Yellow Limonite #40 Bronzite Pyroxenite 5-10% -sbh clear gray 1 Very dark green 0.5 mm Massive BRONZITE 68-73% Brown Iridescent when fresh, mm some have bent cleavage traces. Medium grained. Possible MAGNESITE - 7%, anh, gray, 2 mm, angular, slow reaction to HCl. #41 Dunite 95-97% Green when fresh, orange if weathered 0.8 mm Spheroidal Fine to medium grained. WEATHERING PRODUCTS: Talc Fibrous Serpentine 4

5 APHANETIC TO Plagioclase Olivine Phlogopite Hornblende Ortho- Chromite #42 Kimberlite 3% White to gray 1 mm 40% -sbh Dark green to black mm to Altering to Hematite 2% -sbh Copper Coarse grained. SERPENTINE - 50%,, bluish to greenish-gray, mm, asbestos form common. CALCITE -, anh, white, mm, angular. Talc - soapy white powder Muscovite #337 Harzburgite 4 Dark green to black mm BRONZITE 30% Bronze Iridescent 2 mm Dull to waxy 8% Coarse grained. CALCITE - 12%, anh, white, 1.5 mm, angular. #343 Chromitite 10-1 Serpentinized in places 85-90% High density. 4310LB8HS_S16.wpd December 17,