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Alcove Bluestone

Submitted by Intern on Tue, 2015-03-10 10:55
Stone Type (Commercial): 
Availability: 
Available
Geology
Stone Type (Lithologic): 
Grain Shape: 
Angular
Subrounded
Grain Sorting: 
Moderately-Sorted
Poorly-Sorted
Grain Size: 
Medium
Very Fine
Petrographic Description: 

Specimen: 2015-009-1
This specimen is a sandstone. Detrital grains constitute about 50 to 60 percent of slide area with the remainder occupied by fine grain cementing matrix. There is no appreciable void space. Of the detrital grains, quartz comprises about over 95 percent, but a majority of this is in polycrystalline forms indicative of plutonic, metamorphic, or even arenite rock fragments. Rare feldspar, opaque, and other mafic mineral grains are also present. Based on these estimates this sandstone is classified as a lithic greywacke. The constituent grains are poorly sorted and subrounded to subangular. These observations suggest the parent material was mineralogically (high clay) and texturally (poorly sorted and angular) immature. Maximum lithic grain size is .8 mm and minimum is .02 mm. The modal size is around .5 to .4 mm. The average individual quartz crystal is about .2 to .08 mm. Matrix cement is predominantly clay minerals and mica, there is also a significant amount of very fine grained quartz and perhaps feldspar included in this matrix. This may indicate the presence of small terrigenous clastic lithic grains not discernible from the surrounding cement. No visible macrostructure, such as bedding is visible in thin section. The hand sample presents no appreciable macrostructure that might be visible in thin section.
MP 9/452015

Specimen: 2015-009-2
This specimen is a sandstone. Detrital grains constitute about 50 to 60 percent of slide area with the remainder occupied by fine grain cementing matrix. There is no appreciable void space. Of the detrital grains, quartz comprises about over 95 percent, but a majority of this is in polycrystalline forms indicative of plutonic, metamorphic, or even arenite rock fragments. Rare feldspar, opaque, and other mafic mineral grains are also present. Based on these estimates this sandstone is classified as a lithic greywacke. The constituent grains are poorly sorted and subrounded to subangular. hese observations suggest the parent material was mineralogically (high clay) and texturally (poorly sorted and angular) immature. Maximum lithic grain size is .8 mm and minimum is .02 mm. The modal size is around .5 to .4 mm. The average individual quartz crystal is about .2 to .08 mm. Matrix cement is predominantly clay minerals and mica, there is also a significant amount of very fine grained quartz and perhaps feldspar included in this matrix. This may indicate the presence of small terrigenous clastic lithic grains not discernable from the surrounding cement. Several crystals of what is likely secondary calcite are also present in the matrix. No visible macrostructure, such as bedding is visible in thin section. The hand sample presents no appreciable macrostructure that might be visible in thin section.
MP 9/5/2015

Specimen: 2015-009-3
This specimen is a sandstone. Detrital grains constitute about 60 to 80 percent of slide area with the remainder occupied by fine grain cementing matrix. There is no appreciable void space. Of the detrital grains, quartz based lithic fragments comprise about 60 to 70 percent of grains. These grains are from any number of contexts: plutonic, metamorphic, or even arenite rock fragments. Quartz based grains tend to be subrounded to subangular. Zoned quartz and highly consertal boundaries indicate at least some grains have metamorphic histories. Rare feldspar, opaque, and mafic mineral grains are also present individually and as part of these lithic fragments. There is also a considerable contribution to the detrital grain total of 30 to 40 percent from terrigenous clastic rocks, such as shale or siltstone. These are very hard to distinguish from the matrix material that is composed of essentially the same material, but they tend to have a rounded shape that makes them visible in certain areas of the slide. The difficulty in identifying these grains is the basis for the large compositional range estimates given for this slide. Based on these estimates this sandstone is classified as a lithic greywacke. The constituent grains are poorly sorted. These observations suggest the parent material of detrital grains was diverse and composed of mineralogically immature, or at least contained an immature component in the form of the clastic lithic fragments and significant fine grained material. Texturally the sandstone is also immature. Maximum lithic quartz grain size is .8 mm and 1 mm for clastic lithics. The modal size is around .5 to .4 mm for quartz based grains and .6 to .4 for clastic fragments. The average individual quartz crystal is about .2 to .08 mm, but there are some notably larger exceptions. Matrix cement is predominantly clay minerals and mica, there is likely also a significant amount of very fine grained quartz and perhaps feldspar included in this matrix. There is very faint bedding suggested by the relative prevalence of the two lithic grain components. There is no appreciable macrostructure visible in the hand sample.
MP 9/5/2015

Specimen: 2015-009-4
This specimen is a sandstone. Detrital grains constitute about 40 to 60 percent of slide area with the remainder occupied by fine grain cementing matrix. There is no appreciable void space. Of the detrital grains, quartz based fragments comprise about 80 percent of grains. These are roughly equally divided between monomineralic grains and quartz based lithic fragments. These latter grains are from any number of contexts: plutonic, metamorphic, or even arenite rock. Quartz based grains tend to be subangular to angular. Zoned quartz and consertal boundaries indicate at least some grains have metamorphic histories. Rare feldspar, opaque, and other mafic mineral grains are also present individually and as part of these lithic fragments. There is also a contribution to the detrital grain total of at least 15 to 20 percent from terrigenous clastic rocks, such as shale or siltstone. These are very hard to distinguish from the matrix material that is composed of essentially the same material, but they tend to have a rounded shape that makes them visible in certain areas of the slide. The difficulty in identifying these grains is the basis for the large compositional range estimates given for this slide. Based on these estimates this sandstone is classified as a lithic greywacke. The constituent grains are moderately sorted. These observations suggest the parent material of detrital grains was diverse and composed of mineralogically immature, or at least contained an immature component in the form of the clastic lithic fragments and fine grained material. Texturally the sandstone is also immature. Maximum lithic quartz grain size is 1.2 mm and .8 mm for clastic lithics. The modal size is around .3 mm for quartz based grains and .6 for clastic fragments. The average individual quartz crystal is about .2 to .08 mm, but there are some notably larger exceptions. Matrix cement is predominantly clay minerals and mica, there is likely also a significant amount of very fine grained quartz and perhaps feldspar included in this matrix. In a few areas opaque, presumably iron/manganese rich cement predominates and produces a minimal banding appearance. There is some diffuse clouding and banding present in the hand sample that cannot be definitively tied to any features noted in the thin section.
MP 9/5/2015

Specimen: 2015-009-5
This specimen is a sandstone. Detrital grains constitute about 40 to 60 percent of slide area with the remainder occupied by fine grain cementing matrix. There is no appreciable void space. Of the detrital grains, quartz based fragments comprise about 90 percent of grains. These are dominated by quartz based lithic fragments with a lesser number of monomineralic grains. The polymineralic lithic grains are from any number of contexts: plutonic, metamorphic, or even arenite rock. Quartz based grains tend to be subangular to angular. Zoned quartz and consertal boundaries indicate at least some grains have metamorphic histories. Rare feldspar, opaque, and other mafic mineral grains are also present individually and as part of these lithic fragments. There is also a contribution to the detrital grain total of at least 5 percent from terrigenous clastic rocks, such as shale or siltstone. These are very hard to distinguish from the matrix material that is composed of essentially the same material, but they tend to have a rounded shape that occasionally makes them visible. The difficulty in identifying these grains is the basis for the large compositional range estimates given for this slide. Based on these estimates this sandstone is classified as a lithic greywacke. The constituent grains are moderately sorted. These observations suggest the parent material of detrital grains was diverse and composed of mineralogically immature, or at least contained an immature component in the form of the clastic lithic fragments and significant fine grained material. Texturally the sandstone is also immature. Maximum lithic quartz grain size is .8 mm and .6 mm for clastic lithics. The modal size is around .3 mm for quartz based grains. The average individual quartz crystal is about .2 to .08 mm. Matrix cement is predominantly clay minerals and mica, there is likely also a significant amount of very fine grained quartz and perhaps feldspar included in this matrix. There is some diffuse clouding and banding present in the hand sample that cannot be definitively tied to any features noted in the thin section.
MP 9/5/2015

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