Tapeats Sandstone/Conglomerate
This is a polished face of the speicimen that nicely shows the grains of pebbles.
A very pebble rich portion of the Tapeats Sandstone
Locality: Near Payson, Arizona
Note: Two "Interesting Grains" are identified on the image. They are interesting because they are crystals. Crystal are not commonly found in coarse grained detrital rocks. The reason being is that their environment of deposition is typically high energy as in beaches or streams. Bouncing or rolling along with the other grains in the sediment would round off the points in a crystal. That begs the question how did they form and what are they.
A brief test showed they did not react with hydrochloric acid (so they are not a carbonate) and the hardness is around 7. These properties are consistent with quartz along with their crystal shapes.
The question of how they got there is a bit more complicated. Were they formed in place or deposited along with the other grains? Lack of abrasion would suggest they grew in place, although they both have fractures suggesting impacts or at least stress on the crystals.
Petrographically speaking, they could have grown in voids in the very porous rock. The crystals do appear to include reddish brown matrix of which the host rock has an abundance. Perhaps the fact that their "c" axis are fairly aligned and they are both zone may be an important factor.
Are there other crystals aligned at different angles in this polished face?
Done speculating for now.
Tapeats Sandstone/Conglomerate
This is a polished face of the speicimen that nicely shows the grains of pebbles.
A very pebble rich portion of the Tapeats Sandstone
Locality: Near Payson, Arizona
Note: Two "Interesting Grains" are identified on the image. They are interesting because they are crystals. Crystal are not commonly found in coarse grained detrital rocks. The reason being is that their environment of deposition is typically high energy as in beaches or streams. Bouncing or rolling along with the other grains in the sediment would round off the points in a crystal. That begs the question how did they form and what are they.
A brief test showed they did not react with hydrochloric acid (so they are not a carbonate) and the hardness is around 7. These properties are consistent with quartz along with their crystal shapes.
The question of how they got there is a bit more complicated. Were they formed in place or deposited along with the other grains? Lack of abrasion would suggest they grew in place, although they both have fractures suggesting impacts or at least stress on the crystals.
Petrographically speaking, they could have grown in voids in the very porous rock. The crystals do appear to include reddish brown matrix of which the host rock has an abundance. Perhaps the fact that their "c" axis are fairly aligned and they are both zone may be an important factor.
Are there other crystals aligned at different angles in this polished face?
Done speculating for now.