You will likely need a magnifying glass, in order to fully appreciate the true grandeur of these stones (especially if you are doing the whole DC M&M Trail ). Are you ready?
Total walk (on paved walkways) is about .65 miles.
VIETNAM WAR MEMORIAL
ROCKS & MINERALS STUDIED HERE: Black Indian Granite (Terms: Gabbro, Granite)
LR #1, #2-- N 38 53.456 W 077° 02.894
Logging Requirement #1-- Examine the polished rock face.
Determine:
a. Color and
b. Crystal size.
Logging Requirement #2 -- Based on the descriptions below is this a GABBRO (no visible crystals, high polish) or a granite (visible crystals, especially quartz, high polish) or Basalt (dullish, no crystals, no polish)? NOTE: YOU WILL NEED TO MAKE A NOTE of the details to compare/contrast at your next stop, the Korean War Memorial.
DESCRIPTION
BLACK INDIAN GRANITE
The darkest rock possible was used for the Vietnam Veterans Memorial so that the polished surface would reflect like a mirror. The natural color of the Black Granite from Bangalore, India is the color inside the engraved names, not the color of the polished surface. Can you see big crystals of pink or gray feldspar and clear crystals of quartz inside this rock? If not, it is not really granite.
TERMS:
GABBRO, GRANITE, BASALT:
Gabbro, Granite, and Basalt are formed from magma. When this magma gets trapped in a single intrusive (under the surface) layer, it will GRADUALLY cool, and form gabbro. The texture will be even, the mineral grain size very small. If this same magma gets pushed up from deeper in the earth’s crust (metamorphized), this pressure will force the component materials to coalesce forming larger crystals This is usually a GRADUAL process and intrusive—below ground. If this same magma cools quickly (through contact with air or water – typically extrusive) it will form basalt.
Gabbro is the “blackest” “granite” that is possible – and since most people don’t know what gabbro is, it is usually mined as “black granite.” Basalt can be mined and passed off as gabbro—but only if the miners are dishonest an the purchasers are unknowledgeable about their geology!
KOREAN WAR MEMORIAL
ROCKS & MINERALS STUIDED HERE: Academy Black Granite
LR #3, #4-- N 38 53.263 W 77 02.879
Logging Requirement #3-- compare/contrast the memorial wall with the rock in the memorial wall at the Vietnam Veteran's Memorial. Specifically, are any visible crystals at these coords larger or smaller than those found at "The Wall"?
Logging Requirement #4 -- Based on your answer, is the Korean War Memorial wall a gabbro or a granite? Remember to read the definitions carefully!
ACADEMY BLACK GRANITE:
The Academy Black granite used in this monument was formed during the Jurassic Age, near Raymond, California.
During the Jurassic Age (the age of the dinosaurs), magma at the base of ancient volcanoes in the Sierra Nevada foothills cooled to form this dark grey, almost black, intrusive (inside the ground) igneous rock. Because the granite formed underground, the crystals are small. You will notice Extrusive forms of granite at several other memorials and can thus contrast the size of the crystals and soon "diagnose" whether a granite was formed intrusively or extrusively.
Logging Requirement #5 (also the location for one of the stops of DCNMEPT -- FDR Memorial) The benches at N 38 52.981 W 77 02.522 are also Academy Black Granite, though in an unpolished state. What do you notice about crystal size and luster?
DEFINITION:
Luster: How light reflects off of a rock or mineral types of Luster: Metalic -- Metallic Luster refers to minerals that look like a shiny metal.
Vitreous -- Also called glassy.
Resinous -- Minerals that look like resin (a little bit like the look of plastic).
Pearly -- Minerals with a pearl-like, iridescent luster.
Greasy -- Some minerals look like they have a thin layer of oil on them.
Silky -- Minerals that look like fibers of silk.
Adamantine -- This describes minerals with a brilliant luster, sometimes with colors flashing in the mineral.
Please send your answers. Then post a found log. I will contact you if there are any problems or questions about your answers.
Congrads to captainmath for FTF (First to Finish Logging Requirements) on this earthcache!
References: D4K: Idaho Public Television Discussion for Kids -- Link Kids Love Rocks Link