A Geoscience Digital Image Library
A Geoscience Digital Image Library
| Title | Thin section of nepheline syenite (malignite) |
|---|---|
| Description | This is a photo of a cross polarized thin section of nepheline syenite (malignite). Nearly half of the rock is composed of euhedral to subhedral, elongated, pale brownish-yellow acmite prisms. Simple and lamellar twinning and zoning is present in some crystals, and grains exhibit a somewhat preferred orientation. Low birefringence nepheline and sanidine make up the other essential minerals. Grains are mostly subhedral and commonly intergrown. Nepheline shows a hexagonal outline in some crystals and lacks the cleavage and tabular form of the sanidine. A few percent of pleochroic amber biotite plates are present, in some cases euhedral and zoned. A percent or two of tiny euhedral magnetite makes up the opaques. Occasional large accessory forsterite anhedra are rimmed with bitotite. An occasional zeolite segregation may be present. |
| Location | USA ▹ Montana ▹ Park |
| Photographer | Darla Sondrol. 2002-04-03. |
| Collection | Ward’s Collection of Classic North American Rocks #18. |
| Key words | nepheline, syenite, malignite, Montana |
| Tech details | 959 KB. Thin section. Nikon FDX-35. |
| GeoDIL number | 2563 |
 | |