1. 23. Layers in intrusive rocks. Dan Barker April 2009

2. Many intrusive igneous rocks show layering, expressed as variations in proportions or orientations of minerals, crystal sizes, and, more subtly, in mineral compositions. The causes of such variation are several, including: 1. gravitational sorting (crystals more dense than liquid sink, those less dense rise) 2. flow differentiation (crystals and liquid get separated by variations in velocity vectors) 3. injection of different magmas at different levels within the intrusive body 4. rhythmic precipitation (a magma is saturated with respect to a mineral and precipitates that until it becomes depleted, i.e., undersaturated, and becomes saturated with respect to another mineral) The following images are offered without interpretation, because the origins of layers are commonly ambiguous.

3. Alternating layers of nearly pure chromite and plagioclase, Bushveld complex, Dwars River, South Africa

4. At Dwars River again

7. The last image from Dwars River

8. Chromite-rich layers in peridotite, Addie NC

9. Addie NC

10. Vertical layers in peridotite, Rougemont, Quebec

11. Cross-cutting Layers in syenite. Mt Johnson, Que

12. Layers in syenite, Mt Johnson, Quebec

13. Mt Johnson, Quebec

14. Rhythmic layers, Kringlerne, Ilimaussaq complex, SW Greenland

15. Sunken block of roof rock (arrow), Kringlerne

16. Kringlerne from head of Kangerdluassuq fjord, Greenland

17. Kringlerne

18. Cycles of black, red, and white layers, Kringlerne. Top Base hidden below sea level

19. One cycle of black, red, and white layers, Kringlerne

20. Photomicrograph of black rock. Alkali feldspar and intense blue amphibole

21. Photomicrograph, red rock. Eud is eudialyte, a Na, Fe, Zr silicate that is red in hand sample. Others are alkali feldspar and amphibole. Eud

22. Photomicrograph, white rock. Alkali feldspar is more abundant than eudialyte and amphibole. Eud

23. Layers in another igneous unit of the Ilimaussaq complex, SW Greenland

24. Layers in syenite and granite, just under the roof of the Ilimaussaq complex, Greenland.

25. Layers in Nine Point Mesa intrusion, Big Bend National Park, Texas.

26. Top view of vertical layers in gabbro, Mount Royal, Que.

27. Schlieren in granite, Enchanted Rock TX

28. Enchanted Rock, TX

29. Enchanted Rock, TX

30. Layers in nepheline syenite, Spitskop, South Africa

31. Gently dipping layers in Bushveld complex, Steelpoort Valley, South Africa

32. Phlogopite-diopside-apatite rock, Foskor Pit, Palabora Complex, South Africa

33. Closeup, Foskor Pit

35. Phlogopite-diopside-apatite rock, Foskor Pit, Palabora

36. Rhythmic layering in diorite, Pleasant Bay, ME

37. Mafic layer in sharp contact with granite on right, gradation into intermediate rock on left. Pleasant Bay,ME

38. Layers in gabbro, E. edge of Port Coldwell complex, Ontario

39. Layered gabbro, Centre I, Port Coldwell complex, Ontario

40. Schlieren in ferroaugite syenite, Port Coldwell, ONT

41. Layers in ferroaugite syenite, Port Coldwell, Ontario. Glaciated outcrop, north shore of Lake Superior.

42. Layers in nepheline syenite, Port Coldwell complex, Ney Provincial Park, ONT

43. Nepheline syenite, Ney Provincial Park, Ontario

44. Layers in Centre III, Port Coldwell complex

45. Layered mafic and ultramafic rocks, Garbh Bheinn, Skye

46. "Inch-scale" layers in anorthosite, Stillwater Complex, MT

47. Layered gabbro, Ushuswanna Complex (2874 Ma) So Africa

48. G-3 granite, Soldaatenbaai, Cape Province, South Africa

49. G-3 granite, Soldaatenbaai. R G Cawthorn for scale.

50. G-3 granite, Soldaatenbaai

51. Layers in peridotite, Lers, French Pyrenees

52. Main Donegal Granite, Glen Quarry, Ireland