Rock Id

[frogwizard]

I found these in a rock garden at the house we bought. Any ideas as to what kind they are? The whitish one is smooth on the other side and looks like the inside of a broken brazil nut. Thanks

 

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[allen_idaho]

The first is a piece of agate. The second looks like quartz.

 

[frogwizard]

I thought agates all had colorful patterns inside. This one is a uniform color inside. I know the purple is amethyst.

 

[kbrocks]

I would say that the lighter colored stone is Flint or Chert. It is a very close relative of Agate. For what it's worth, not all agates are colorful, it really depends on the type. But that pale creamy color stone you have looks like a lot of the West Texas Flint I have.
The second one, I'm not sure. I have a few like it in my rock pile but never gave them much thought. I've tried tumbling them and they didn't turn out too well.

 

[cerF]

Chert, flint and agate are all quartz, but are sedimentary varieties of it, with quartz itself being an igneous mineral. The rock in question looks to be a chert to me. This is evident due to the glassy texture, lack of visible crystal structure and the conchoidal (rounded) fractures which are very indicative of quartz.

Its hard to tell from the photo, but the darker one could possibly be an andesite or gabbro, with associated quartz or a calcite interior. Id have to see it n person to give a definitive answer though.

The purple one is amethyst (quartz).

HH