What are these made of?

[Essex]

From time to time I stumble across these type knives, etc. with the white/grayish color. What is it called?

 

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[willjo]

Center one looks like Coastal plain chert, bottom one looks like Rhyolite, and others look like a poor grade of coastal plain. Hope this helps and someone may be more familiar with it and give you a better answer.

 

[rock]

Although willjo acts like he isnt a expert dont let him fool you he is. I think he nailed those types for you. Nice points

 

[Essex]

I'm trying to learn more about my collection and your input is invaluable. Thanks!