In the United States and Canada, the name "diabase" is used for a dark gray to black, fine-grained, intrusive igneous rock that has a composition similar to basalt and gabbro. The difference between basalt, diabase, and gabbro is in their grain size - which was determined by their cooling rates.
It was intruded as a liquid magma 200 million years ago when North America drifted away from Europe and Africa.
Basalt: rapid cooling in a lava flow produced individual crystals that are so small they are difficult to see with the unaided eye.
Diabase: slower cooling in shallow intrusions such as sills, dikes, or laccoliths allowed individual crystals to grow slightly larger - up to about two millimeters in size.
Gabbro: slowest cooling below Earth's surface gave crystals a longer time to grow - some may be over a centimeter across or larger.
In the United Kingdom and a few other countries, diabase is known as "dolerite". The two words are synonyms.
The parent magma of the rock began cooling slowly, deep underground, and some large crystals of minerals with a high crystallization temperature began to form there. The magma was then erupted to the surface or moved to a shallow location, such as a dike or sill, where the next, and often the final, part of its cooling occurred. The cooling rate at this shallow depth was faster and the groundmass of the rock is composed of small crystals of minerals that have a lower cooling temperature.
Much diabase contains two distinctly different crystal sizes and is known as "diabase porphyry". When cut and polished, it can make an interesting and attractive stone for use in tiles, countertops, window sills, stair treads, facing stone or other uses.
At Ground Zero is a information sign using that, what you have read and onsite observations ANSWER THE QUESTIONS AND SEND THEM VIA GEOCACHING DO NOT POST THEM IN YOUR LOGS !!
1. Whats the diffrence between Diabase , Basalt and Gabbro ?
2. What Happen 200 Million years ago to cause this ?
3. Feel the rocks are the rocks how do they feel ?
4.When they cut thru here to make the railroad how high is the top of the cutout.
5.what are the 4 rock types explained on the cross section of info sign ?
6. Do you see any Grallator fossils some have been found in the area ?
7. Post a picture of you, face not required or a personnel object at Ground zero with rock wall behind.