Rock of the Week #7

Here's a fun one I collected Long Ago.
1. What is the large fossil (meaning the big round thing on the right side of first photo)?
2. Name this rock (any appropriate classification scheme is OK.)
3. Multiple choice. This rock is:
a) Proterozoic
b) early Paleozoic
c) late Paleozoic
d) Mesozoic
e) Cenozoic
f) Quaternary (modern)

Solution to Rock of the Week #6:

This rock is only 500 years old! It erupted from Panum Crater, a small rhyolitic cone in the Mono-Inyo chain in California’s Long Valley Caldera. Legends among the local Inyo tribe of the Native Americans reveal that the eruptive event was observed by local residents. The Mono-Inyo volcanics are about 76% SiO2, with only rare phenocrysts, producing pumice and obsidian. Both are glassy products but with variable bubble contents. The pumice (like this sample) can be very low density! It can be found floating on nearby Mono Lake. Nobody can resist picking up huge rocks of pumice and lifting them over head.
Here's an example from Tulane's 2002 trip.

1. (1 pt) What is rock?
: 1 point given for pumice.

2. (2 pt) How did it form?
: 1 point for volcanic.
: 1 point for rhyolitic or dome or crater.


Callan Bentley said...

Receptaculid (a.k.a. sunflower "coral") - early Paleozoic. That's the best one I've ever seen...

Silver Fox said...

My standard paleonotology "guess" has long been Ordovician - but I see that isn't listed as one of the possibilities. (As a guess, it worked well - sometimes - in Virginia; it probably wouldn't work so well in other areas!)

Trifarina said...

Yea for hash!