Leaverites

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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What is a Leaverite?

It's any oddball feature in a rock that can't easily be named or found in a textbook. As in "Leave 'er right where you found 'er." The general rule with rocks is "when you see hoof prints, think horses, not zebras." Novices tend to jump to exotic explanations first; geologists look for commonplace explanations.

Common Types of Leaverites

Since these are odd or unusual and found by people who don't know what to call them, and often don't even know where to start looking for answers, there is no easy way to classify them. It's like looking up a word in the dictionary if you don't have a clue how to spell it. Browse the list below and follow the links to other pages to see if anything works for you.

Man-Made Features

Man-Made Coatings
Don't overlook the possibility that a strange marking on a rock may be due to paint, asphalt, adhering concrete, oil, lime, fertilizer, or some other artificial material.
Man-Made Markings
Grooves and scratches on rock surfaces can be due to bulldozers, backhoes, logging cables, etc. Tires will leave black films on rocks.
Tumbling
The rounded shiny stones you can buy in souvenir stores are created by tumbling in a barrel full of abrasives. A few weeks with a week or so at successively finer abrasive grades will do it. Sometimes natural stones can be well rounded, even a bit shiny, but rarely as shiny as artificially tumbled stones.
Dyed Stones
Some stones are naturally brightly colored, but if the color is extreme, consider the likelihood that it could be a dyed stone.
Cut surfaces
Around old quarries, rock shops, and other places where people work with stone, cut pieces are common. If the surface is extremely flat, it's almost surely cut. Parallel curved markings on the surface are saw marks, but polished surfaces won't have them. Tumbled stones in rock shops frequently started as cut slabs. If they're very thin and flat, or have flat parallel opposite sides, that's what happened.
Drill holes
Smooth, extremely circular holes in rock are drill holes. In stone blocks, it's common to see regularly spaced partial drill holes which were used to split the stone.
Drill cores
Round rods of rock are probably drill cores. In old mining areas they can be very common and piles of them may be lying around. They are cut with a hollow pipe with diamonds embedded in the end and are used for gathering samples for study. Often the less interesting rock is just left on site.
Blasting
Blasting leaves radiating fractures around the blast site. Often a drill hole is visible at the center.

Unrocks (Artificial Materials)

It's astonishing how many artificial materials can be mistaken for rocks. Always suspect artificial materials in any urban location or anyplace where there has been human activity. Even in apparently pristine areas there may be ruins of old buildings.

Rounding
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.
Taconite Pellets
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.
Concrete
Gravel cemented together. Flat surfaces usually indicate a form. The natural sedimentary rocks conglomerate or breccia can look a lot like concrete, because concrete is artificial conglomerate or breccia.
Asphalt
The black matrix is a dead giveaway. Also, tends to flatten rather than shatter when hit with a hammer.
Brick
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
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.
Slag
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.
Clinker
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. Waste piles around coal mines can catch fire and create large piles of clinker. Natural clinker occurs where burning underground coal seams melt adjacent rocks.
Glass
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.
Porcelain
Usually white or light colors, with a fine granular texture on broken surfaces.
Metal
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.
Sulfur
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.
Plastics
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.

Veins

No single feature in rocks attracts as much attention from non-geologists as veins

Surface Markings

Dirt
Believe it or not, many people don't realize they have to clean the dirt off a rock to tell what it is. So give any unusual rock a good scrubbing first. That odd marking may just be stuck-on soil.
Wetness
Wet rocks look darker than dry ones and may often reveal subtle features better. This is because small surface imperfections that scatter light are hidden by a film of water. Polishing or a coat of varnish can often preserve the wet appearance.
Burial
If the rock was partially buried, half of it will be clean and the other half covered with dirt. If the rock has a sharp boundary and one half looks dirty or earthy, this may be why. Scrub the soil off.
Moss, Lichens, and Micro-organisms
Crusty stuff on a rock is probably lichens and even a wire brush won't remove it. Some lichens are brilliantly colored red or yellow. Green stains on or within a rock, especially in damp settings, are often algae, not a mineral. Black stains may be organic carbon or micro-organisms, too.
Water Markings
Rocks that have been half immersed in water may have a line around the rock marking the water line. The line may be accented by white powdery films, which may be due to suspended mud or dried algae. Yellow powder may be pollen, which floats on the surface of the water.
Precipitates and Surface Films
Lots of rocks are covered with thin films of material leached out of other rocks or soil.
Iron Oxide
Red, orange, or brown coloring is often due to iron oxide. The iron oxide is usually derived from weathering of other minerals or man-made objects.
Sulfur
Sulfide minerals weather and often liberate free sulfur, which creates a yellowish-green coating. It may well be accompanied by a sulfur smell and iron oxide stains.
Swirly Layers
Layers in a rock may look very convoluted from some angles because of the irregular surface. Turn the rock and see if the layers look flat from a different viewing angle.
Liesgang Rings
These are swirly red or brown bands in rock created by iron oxide solutions moving through the rocks. They may just be surface features on fracture surfaces or they may extend into the interior of the rock.
Tarnish
Metallic minerals often develop a tarnish. It may be multi-colored (iridescent) or just dull. Often fracture surfaces within rocks have thin films of dissolved minerals on them.
Glacial Markings
A wide variety of features caused by glacial action. Most commonly the rock is smoothly planed off. It may even have a shiny polish and usually shows scratches or striations that indicate the ice movement direction.
Slickensides
Thin films of smeared-out minerals, usually with a grooved or linear texture, caused by fault movement. It need not be a major fault; slip of a few inches can do it.
Scorching
Rocks exposed to fire are often black on the surface, or may be oxidized to a distinctive brick red color.
Weathering Rinds
Weathering often affects only the surface of a rock and a cross-section will expose a very different material inside.

Features in Sedimentary Rocks

Ripple Marks
Undulating surfaces on bedding planes caused by waves or currents while the rocks were being deposited.
Mud Cracks
Polygonal patterns resulting from the sediment drying and shrinking before it was buried. These often have rims of whatever filled the cracks.
Cross-bedding
Usually seen on surfaces that break through the rock layers. Within the layer are smaller slanting layers caused by shifting patterns of erosion and deposition. Wind and water action can both produce cross-bedding.
Graded Bedding
Layers where coarse material grades into finer material toward the top, usually caused by fast-moving water that slows down. Floods and submarine landslides are common causes.
Salt Crystal Casts
Relatively rare. These are square or angular impressions left by salt or gypsum crystals as sediment dried out.
Raindrop Prints
Small dimples or craters caused by rain or perhaps hail while the sediment was still soft and exposed on the surface.
Stylolites
Extremely irregular zigzag lines in limestone or dolomite. They mark where material has been removed by solution, leaving insoluble residue to mark the solution zone.
Omars
Omar is short for Omarolluk. The Omarolluk Formation occurs in the Belcher Islands of Hudson's Bay. Round calcareous concretions occur in a fine-grained metamorphosed siltstone. When they weather out, they leave hemispherical holes. These rocks are only known to occur in a small area in Hudson's Bay but the glaciers spread them across central Canada and into the northern U.S.

Fossils, Pseudofossils, and Related Things

Real Fossils
As a general rule, if you think it might be a fossil, it probably isn't. If it's so clear even a novice can recognize it, it is.
Petrified Wood and its Look-Alikes
Metamorphic rocks in particular can have very linear textures that result from the rock being stretched. These can easily be mistaken for petrified wood.
Fossil Eggs
That unusually round pebble is not a fossil egg. Real fossil eggs are found in sedimentary rock layers associated with fossil bones, very often in clusters or nests. Almost always the shells are fractured and often the skeletons of the unhatched young are still inside. Unless you have all those things, it's not a fossil egg. They are not found as isolated round pebbles.
Fossil Hash
Not the corned beef kind, but broken shells. If you have a rock with lots of small, flat or curving fragments in it, it's probably due to broken up shells.
Burrows
Elongated markings within rock layers are often burrows of aquatic organisms that were filled in by some other material.
Tracks
Organisms browsing the bottom may leave grooves in the sediment. Sometimes the overlying layer preserves a replica of the tracks and we see small ridges in relief.
Dendrites
Often mistaken for fossil moss or fern leaves. These are crystals of iron or manganese oxide something like the patterns frost crystals make on windowpanes. The ornamental variety of dendrites in quartz is actually called moss agate.
Concretions
A wide variety of odd shapes found in sedimentary rocks, and with a variety of origins. Usually something in the rocks causes the chemistry nearby to change, affecting how the rock is cemented. Sometimes a fossil starts the process, but a concretion itself is not a fossil.
Geodes
Hollow cavities in igneous or sedimentary rocks that fill with quartz. They may be lined with crystals, may be filled by concentric layers of agate, or may have horizontal layers inside.
Sand Crystals
These occur in sandy soil where calcite or gypsum crystals enclose sand grains. They cement the sand grains together but the form of the sand preserves the form of the crystal.
Chert Nodules
White chalky masses or gray glassy nodules often found in limestone and dolomite. They are often mistaken for fossil bones. Real fossil bones are usually dark brown, not white.
Omars
Omar is short for Omarolluk. The Omarolluk Formation occurs in the Belcher Islands of Hudson's Bay. Round calcareous concretions occur in a fine-grained metamorphosed siltstone. When they weather out, they leave hemispherical holes. These rocks are only known to occur in a small area in Hudson's Bay but the glaciers spread them across central Canada and into the northern U.S.

Features in Igneous Rocks

Phenocrysts
Large crystals in an otherwise fine-grained rock
Flow Banding
Streaks due to flow of lava or magma
Pillows
Rounded masses of lava caused by sudden cooling upon contact with water
Orbicular texture
Round clusters of crystals, sometimes with a bulls-eye pattern, in granite
Vesicles
Cavities due to gas bubbles in the lava (rarely, magma)
Pahoehoe
Ropy surface texture on lava flows
Aa
Rubbly surface texture on lava flows
 

Features in Metamorphic and Deformed Rocks

Large Crystals (Porphyoblasts)
Foliation
Folds
Kink Bands
Boudinage
Foliation
Folds
Kink Bands

Weathering Features

Differential Weathering
Differing amounts of weathering cause different rocks to stand out in relief.
Solution
oihe
Exfoliation
The rock peels away in thin layers like an onion
Cavernous Weathering
Weathering Rinds
Weathering often affects only the surface of a rock and a cross-section will expose a very different material inside.

Fractures

Conchoidal Fracture
Glassy materials break with a distinctive curving fracture.
Radial Fracture
Some minerals grow as radiating bundles of fine, fibrous crystals.
Fibrous Fracture
Minerals that grow as parallel bundles of fine, fibrous crystals give the rock a fibrous look when it breaks.
Joints
Planar cracks found in almost every rock due to small near-surface stresses in the crust
Columnar Joints
Lava flows, and occasionally thin sheetlike intrusions like dikes and sills, shrink as they cool and break into polygonal columns.
Plumose Fractures
Most joints display a fan-like ribbed texture that forms during the fracturing process
Shatter Cones
Rare but very significant conical fracture surfaces that occur at meteor impact sites.

Meteo-wrongs

People tend to mistake terrestrial rocks for meteorites. Commonly mistaken objects include:

Artificial Materials
Slag and waste metal are especially often mistaken for meteorites. Meteorites do not melt except for a thin surface layer. They do not flatten against the surface they hit, or enclose objects they hit. If it's obviously flattened against a surface or encloses terrestrial objects, it is not a meteorite.
"Melted" Rocks
Meteorites develop a thin fusion crust while entering the atmosphere, but  people often mistake any shiny surface for melting. Volcanic rocks, of course, really were molten. Other shiny surfaces can be due to weathering or mechanical action.
Unusually Dense Rocks
Most rocks fall in the density range of 2.5 to 3 times as dense as water, and rocks at the upper end of the range are noticeably denser than those at the lighter end, even just hefting them by hand. Some dark igneous rocks can have densities of over 3 times as dense as water, and iron formations can be five times denser than water. Real meteorites are dense, but density alone doesn't make a meteorite
Magnetic Materials
Many artificial materials are magnetic, but so are magnetite and a number of other minerals. A lot of magnetism is wishful thinking. I've seen people claim that completely non-magnetic materials "seem" to attract a magnet. If the magnet doesn't stick to the material when you turn it upside down, it's not magnetic.
Rocks with Cavities
Real meteorites do not contain internal cavities. The famous meteorite on display at the American Museum of Natural History in New York does have deep surface pits from weathering, but that's how most cavities in rocks form. Cavities alone do not make a meteorite.
Unusual Weathering
Oddly weathered rocks are often mistaken for meteorites

It's Not a Meteorite If...


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Created 22 April, 2005, Last Update 14 December 2009

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