Cape York - The "Lakelands", Starting sol 2703 |
Cape York - The "Lakelands", Starting sol 2703 |
Sep 1 2011, 04:30 PM
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Senior Member Group: Moderator Posts: 4279 Joined: 19-April 05 From: .br at .es Member No.: 253 |
Bye bye, Tisdale. It's time to move on.
Next target? Philosilicates. ----- Edited on Sep 16 2011. This thread is dedicated to the exploration of Cape York, starting on sol 2703 when Opportunity left the "rocky garden" and started moving towards Chester Lake. |
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Sep 22 2011, 04:48 AM
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Senior Member Group: Members Posts: 2228 Joined: 1-December 04 From: Marble Falls, Texas, USA Member No.: 116 |
... Over time, a glass can weather or degrade from a "glassy" form to a "crystalline" form, a process called "devitrification". In obsidian samples, this is seen as "snowflake obsidian". It could devitrify into a smectite or a clay mineral, but I've seen no suggestions at Salisbury1 of devitrification of the impact melt. ... At this point, even though it appears likely, we really don't know if we are seeing impact melts or not. But the point I was trying to make regarding devitrification was that after about 4 billion years any volcanic glass that may have existed should have had ample time to devitrify. Have you ever seen a Precambrian glass? ... And, picking nits, obsidian is a siliceous rhyolytic glass which is not compatible with the mafic (silica-poor) basalts we see in this region of Mars, so we're looking for glass of basaltic composition, such as a tachylite. ... I understand that we are expecting to see basaltic rocks here, but we don't "know" that all of the rocks here are mafic. Some silicic volcanics would probably be a very exciting discovery on Mars, but I was simply acknowledging Fran's observation that the current science target does resemble an outcrop of obsidian in a perlite matrix. We have to remember that we are among the first geologists from our planet to have had the opportunity to explore the rocks of another. We should expect to be surprised as often as we find things that are familiar. N.B: The perlite used in hydroponics and soil conditioning may be derived from the rock known as perlite, but it is not the same thing. -------------------- ...Tom
I'm not a Space Fan, I'm a Space Exploration Enthusiast. |
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