Earth Science Conservation Review

Summary Full report
Mournes - Diamond Rocks - Mineralogy
Site number:540  
ESCC:EO
Locality Type:Crag, Crags, Scree Status: ASSI
Grid Reference: J325289 Approximate
County: DownCouncil area:Newry, Mourne & Down District Council
Period:Tertiary
Stages:Eocene, Palaeocene
Lithostrat:Granite, Mourne Mountains Granites
Site Description

The Diamond Rocks, Mourne Mountains, Co.Down, May 1997.
Highlights:
Classic locality for crystals of smoky quartz, feldspars, biotite, topaz and beryl in drusy granite.
Introduction:
The Diamond Rocks site, designated as an ASSI in 1999, is described by Dr. J. Preston in Key Site 1110 - Mournes - The Diamond Rocks [Igneous/Tertiary Block]. It is one of the best known localities for minerals from drusy cavities (Emeleus and Preston, 1969): the Ulster Museum has abundant material from the Diamond Rocks and the locality is represented in many other museums.
Description:
The site comprises conspicuous crags of granite and scree (largely man-made) on the southern slopes of Slievenaglough about 100m north of the Brandy Pad path. Dr. Preston considers that the locality was named because of the abundant crystals of smoky quartz present in the drusy granite, but it is probably named because of the less common, colourless and transparent crystals of topaz. Green hexagonal prisms of beryl can also be found, and occasionally blue aquamarine. Crystals of zinnwaldite (brown lithium mica), green fluorite, black tourmaline, Fe-Ti oxides and stilbite occur very infrequently in the drusy cavities. Books of biotite mica and well-formed crystals of both orthoclase and albite are as abundant as smoky quartz. Crystals are typically 3-10mm in size. Geochemical analyses indicate that the drusy granite is enriched by factors of 2-4 in uranium and thorium in comparison with normal (G2) granite. The concentration of such elements as U, Th, Li, Be, B and F and the presence of cavities is interpreted as evidence for upward migration of watery fluids during crystallization of the granitic magma, and trapping of the fluids beneath a previously-solidified roof of the intrusion.
Interpretation:
The concentration of such elements as U, Th, Li, Be, B and F and the presence of cavities is interpreted as evidence for upward migration of watery fluids during crystallization of the granitic magma, and trapping of the fluids beneath a previously-solidified roof of the intrusion.
Notes:

See also Key Site 1110 - Mournes - The Diamond Rocks.

Keywords
Minerals:Beryl, Fluorite, Quartz, Stilbite, Topaz, Tourmaline, Zinnwaldite, Aquamarine
Rocks:Granite
Structures:drusy
Access
Approach:Mountain outcrops accessible only by hill-walkers.
Management:
The Diamond Rocks, Mourne Mountains, Co.Down. May 1997: scree.
In recent years (since the mid-1990s), the volume of scree material has increased noticeably and there is other evidence of systematic working to obtain specimens from the site. While the quantity of bedrock material is probably large and the resource is unlikely to be exhausted, aesthetic damage to the site is a real concern. This should be monitored and preventative action should be taken if necessary.
References
Rec Type ESCR report Recorder: R. Nawaz and N.R. Moles
Enterer: E M Porter
Updates: 07 MAY 68 / 14 Jul 2006 / 22 Sep 2003 / 15 Sep 2003 / 18 JAN 0
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