Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay
It's astonishing how many artificial materials can be mistaken for rocks.
Don't let the fact that the material is rounded like a natural pebble fool you. It only takes a few years on a beach or a few miles of river transport to round rocks and their artificial counterparts.
| These are also round and found along every railroad track in the country. These transformed iron from a limited resource to an unlimited one by making it possible to smelt low-grade iron ore. The screen view is near actual size. |
The problem in the 1950's was that supplies of really rich iron ore were within a few decades of running out. Low grade ore is abundant, but after separation from silicate rocks, it is so fine-grained it would simply be blown out of any blast furnace. Taconite pellets changed all that by converting the fine-grained ore into a form that is easy to ship and handle and heavy enough to stay put in a blast furnace.
Gravel cemented together. Flat surfaces usually indicate a form. The natural sedimentary rocks conglomerate and breccia can look a lot like concrete.
Concrete setting is not simply a matter of drying out. Some concretes harden under water. The cement (lime plus clay) reacts chemically with the sand and gravel to make a synthetic rock.
The flat surface is usually due either to the form used in casting the concrete, or perhaps to some other flat surface the concrete once adhered to.
|This material is a very lightweight, porous concrete used in Europe in settings where light weight and insulating ability are important and strength is not a critical factor.|
The black matrix is a dead giveaway. Also, tends to flatten rather than shatter when hit with a hammer.
Easily mistaken for some volcanic rocks, especially old or decorative bricks with mineral crystals or fragments within them. Usually red, brown, yellow, or tan.
Tile is a generic term for any thin ceramic building material and thus includes a lot of materials. Roofing tiles tend to be very brick-like in appearance. Vitreous tile, used in plumbing, is shiny on the surface and usually curved.
The fused silicate residue from smelting ores. Often similar in composition to natural igneous rocks and can be hard to tell from them. Ropy textures on the surface are common, as are shiny or iridescent tarnishes. Makes great road fill and commonly used that way where available.
The fused silicate residue from burning coal. Has lots of bubbles or vesicles, often inclusions of brick fragments, pebbles, and other debris. Colored tarnish or films on surfaces are common.
Tumbled glass in streams and on beaches is usually translucent, frosted, and has curved surfaces reminiscent of the bottle it came from. Decorative bulk glass is often brightly colored with swirls. Waste glass from crucibles or glass melted by fires may be black and might have bands of frothy material. Some slag is glassy.
|The glass at right contains bands of frothy material.|
|This material, sold as "sunstone" and other names, is a decorative glass often cut as a synthetic gemstone.|
|The material at right is extremely frothy and very similar to pumice, but is artificial.|
Usually white or light colors, with a fine granular texture on broken surfaces.
There are any number of reasons why a metallic object may not show obvious signs of artificial origin. It could have been crushed or otherwise deformed beyond recognition, shattered by impact or explosives, or melted by fire, lightning, or power line failure. It could be foundry waste or welding spatter. If there's a conspicuous flat surface, that may be a sign that molten metal was poured onto the ground or a floor. Also, look for embedded artificial objects.
| Right: From the back, this hunk of fused metal could be confused with a rock |
Below: From the other side, the embedded objects give away the artificial origin of the material.
|Below: This unusual material is iron stalactites, grown from iron vapors in an old iron smelter. The blades are iron crystals.|
|Sulfur is sometimes found on railroad tracks or near industrial plants. Most of it in the U.S. is melted out of subsurface rocks using steam, piped to the surface, and poured into bins to harden. So although sulfur occurs as a true mineral, most chance occurrences of it are artificial.|
Usually recognizable by their lightness and colors. Also, since they are poor heat conductors, they won't feel as cool as other materials. High-density plastics, especially those with mineral fillers, can be harder to tell apart from rocks.
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Created 15 October 2009, Last Update