1-There are 18 volcanoes in the US with the potential to erupt again, all of them in Alaska, Hawaii and the West Coast states.
2-Rubies and sapphires are actually the same mineral - corundum. The basic chemical formula of corundum is Al2O3, but traces of iron stain the mineral red (ruby) while traces of chromium or titanium stain the mineral blue (sapphire).
3-Rubies, sapphires and emeralds are all more rare than diamonds.
4-Not all diamonds are transparent. They come in a variety of colors (called "fancies"), including yellow, green, blue, orange, brown ("champagne"), purple, grey, black (called carbanado, recently shown to be meteroic), milky white, pink, and red. Red is by far the rarest.
6-Will Yellowstone spawn a "supervolcano" that will destroy the US? ANSWER: Probably not. The amount of rhyolitic magma just beneath the surface of Yosemite is relatively small at present, so even if it eventually "erupts" through the surface, should cause minor lava flows rather than a large supervolcano-type eruption. (For those who are still hoping the Mayans were onto something, however, a supervolcano-type eruption is technically possible. USGS sets the odds of such an event occuring in the next few thousand years at 0.00014% .)
7-The Gulf of California is a spreading zone - many millions of years from now, it will be an ocean.
8-The earth is slipping along the San Andreas fault at a rate of about 2" per year. This means that in about 15 millions years Los Angeles and San Francisco will be neighbors.
9-The Great Lakes, combined, contain more than 20% of the world's available fresh water. (Doesn't count underground aquafers or polar ice)
10-People experiencing earthquakes in the Great Lakes region have the glaciers to thank - the earth there is still "rebounding" from having been smushed by glaciers during the last ice age. ("Smushed" isn't actually a geological term, but it should be.)
11-What country owns Antacrtica? ANSWER: No one - there's a treaty that establishes Antarctica as a "neutral zone" ... though no telling how much longer this will go unchallenged, since melting due to global warming has begun exposing huge oil reserves beneath Antarctica's surface.
12-People who wade into the Dead Sea automatically float. Dissolved salts make the water so dense, humans are less dense in contrast and so float.
13-What is the most earthquake-prone state in the US? ANSWER: Gotcha! It's not California, but Alaska.
15-Iceland looks huge on a regular map, but it is approximately the size of Kentucky. This is because the Mercator projection map we use to make lines of latitude and longitude lie flat inadvertently makes countries nearer the poles appear HUGE.
16-Why doesn't the earth have as many craters as the moon? ANSWER: We do - but our craters have gradually eroded away or been overgrown by vegetation.
17-About 200 million years from now, Asia and America will collide to form a supercontinent centered around the north pole. Scientists already have a name for it: Amasia. (Because apparently scientists are better at predicting stuff than they are at naming stuff.)
18-Every so often our magnetic poles "reverse" - the north pole and the south pole reverse their magnetism. Scientists estimate this could happen again about 1000-2000 years from now. (So start relabelling your magnets now!)