Scoria Rock
There are two types of Scoria Rock. The following is what I found on the Geology.com website: Scoria is a volcanic rock containing many holes or vesicles. It is generally dark in color (generally dark brown, black or purplish red), and basaltic or andesitic in composition. Scoria is relatively low in mass as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity greater than 1, and sinks in water. The holes or vesicles form when gases that were dissolved in the magma come out of solution as it erupts, creating bubbles in the molten rock, some of which are frozen in place as the rock cools and solidifies. Scoria may form as part of a lava flow, typically near its surface, or as fragmental ejecta (lapilli, blocks and bombs), for instance in Strombolian eruptions that form steep-sided scoria cones. Most scoria is composed of glassy fragments, and may contain phenocrysts.
The word scoria comes from the Greek σκωρία, skōria, rust. An old name for scoria is cinder.
Scoria differs from pumice, another vesicular volcanic rock, in having larger vesicles and thicker vesicle walls, and hence is denser. The difference is probably the result of lower magma viscosity, allowing rapid volatile diffusion, bubble growth, coalescence, and bursting.
Scoria rocks are igneous rocks which were formed when lava cooled quickly above ground. You can see where little pockets of air had been. Scoria is actually a kind of glass and not a mixture of minerals.
Scoria has several useful characteristics that influence how it is used. It is somewhat porous, has high surface area and strength for its weight, and often has striking colours.
Scoria has several uses:
(1) It is often used in landscaping and drainage works.
(2) It is also commonly used in gas barbecue grills.
(3) Scoria can be used for high-temperature insulation.
(4) Scoria is used on oil well sites to limit mud issues with heavy truck traffic.
(5) It is also used as a traction aid on ice and snow covered roads.
The second description is from the kiosk found near GZ and from a local engineer:
Scoria MAY NOT be a volcanic rock. It is formed when coal beds catch on fire and burn the overlying rocks and melts them into a slag type material.
TO LOG THIS EARTHCACHE:
Please email me the answers through my profile to the following questions:
1. Estimate the number of "bubbles" created within a square foot in the sample at the posted coordinates? And what caused them?
2. Lightly feel the surface of the boulder and describe the texture of the surface. What does it feels like? Is it smooth, rough, or porous?
3. Optional: Take a picture of one of the samples of scoria rock here with your GPs in it.