A Geoscience Digital Image Library
A Geoscience Digital Image Library
| Title | Thin section of nepheline syenite (malignite) |
|---|---|
| Description | This is a photo of a plain 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 the 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, and in some cases are 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 | 822 KB. Thin section. Nikon FDX-35. |
| GeoDIL number | 2562 |
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