A Rockhound’s Glossary
A
Amphibole
A type of silicate mineral that includes actinolite, hornblende, tremolite, and other minerals that contain iron and/or magnesium and are usually found in igneous or metamorphic rock.
Anthracite
The highest grade of coal, which has the most carbon in it and is the hardest and shiniest.
Asterism
Showing a star shape inside the mineral, usually when polished, such as a star sapphire.
B
Batholith
A large deposit of rock that forms when a large amount of magma rises up underground but cools and turns into rock instead of pouring out on the surface as lava. According to the United States Geological Survey (USGS), it has to be at least 40 square miles across to qualify. Many examples we know today, like the White Mountains Batholith in New Hampshire, are above ground after millions of years of tectonic plate movement, erosion, etc., revealed them.
Bedrock
Rock that’s attached to the earth. It’s the solid rock under any dirt, sand, gravel, boulders, etc.
Beryl
A type of gemstone that includes several well-known varieties, such as aquamarine, emerald, heliodor, and morganite.
Black sand
When gold panning, the material that’s left in the pan when all of the lightweight rock and sand have been washed out, usually leaving magnetite and garnet…and hopefully gold.
Borg
A race of semi-artificial non-Earth people who conquer planets and absorb the planets’ people (physically) and knowledge (mentally).
Botryoidal
A rounded and blobby crystal shape that’s made up of thin crystals tightly bunched together, like rays of light from the sun or the tiny parts of a floret of broccoli. Many minerals can have a botryoidal form, but some common ones are prehnite, wavellite, malachite, and smithsonite. The word is pronounced like “ba-tree-oy-dull” and comes from the Greek word for “a bunch of grapes.”
Breccia
A type of rock made up of broken-up pieces of other rocks that are stuck together into new rock. This is similar to conglomerate but with sharp-edged rocks inside, instead of conglomerate’s rounded rocks.
C
Cabinet specimen
A mineral specimen about 4 inches or larger in size.
Cabochon
A piece of a mineral or rock that has been trimmed and ground away and polished until it forms a usually circular or oval dome shape. Cabochons are often used in jewelry, such as necklaces.
Calc-silicate
A mineral that contains both calcium (Ca), the “calc” part, and silicon (Si), the “silicate” part.
Carbonate
A mineral that contains what’s called a “carbonate ion” (CO3), which is a combination of carbon and oxygen, along with one or more other elements. Calcite is the most common example.
Cave pearl
A ball-shaped mass that’s usually made of calcite and forms naturally in pools of water inside caves.
Chalcedony
A type of quartz that is usually mostly opaque and has a cryptocrystalline form. This type includes several well-known minerals, such as jasper, agate, chrysoprase, and onyx.
Chatoyant
Having a sheen that looks like the vertical, line-shaped pupil of a cat’s eye, which seems to stay in place and look at you even if you move the mineral back and forth. This effect usually shows best in a cabochon. Translated from the French, the word means “cat-eye-like.”
Core
The very center of the Earth. The outer part of the core is liquid melted rock. The inner part, the very center of the center, is solid and is made of mostly nickel and iron. Together, the two parts are about 2,100 miles thick, measuring from the center outwards.
Corundum
A type of mineral that is very hard–second only to diamond–and includes two valuable gemstones: ruby and sapphire.
Country rock
In a mine or quarry area, the rock that you don’t want that doesn’t contain the minerals you’re looking for, which surrounds the rock that contains the minerals you do want.
Crust
In terms of the Earth, this is the layer of rock that starts at the surface we’re on and extends downward for at least 3 miles (where it’s under the ocean) and as much as 60 miles or more under the largest mountain ranges. Below the crust are the mantle and the Earth’s core.
Crypto-crystalline
For this type of crystallization, we don’t mean “crypt-ocrystalline,” like crystalline things where dead people are kept, but “crypto-crystalline,” like crystals that are a mystery (as in “cryptic”). That’s because the crystals in this case are tiny little grains you can’t see—which makes them mysterious—and they’re packed together very closely. When you look at a cryptocrystalline mineral, you just see a smooth surface, not sharp-edged crystals. Minerals that have this kind of crystallization look like they’re massive. You can’t see a nice crystal shape, they might just be shaped like a plain old rock, and they’re often opaque. (see also Massive)
Crystal
A usually mostly pure piece of a mineral that has naturally formed crystal faces (or “facets”).
Crystal system
(see Shape)
D
Desert rose
This type of crystal habit occurs when minerals in dry desert areas solidify in a shape that looks like the petals of a flower and some of the sand there gets included in the petals. It looks like a flower made of sand. (see also Mineral rose)
Dike
A deposit of rock that fills a crack that crosses layers of a larger rock deposit. (see also Sill)
Double refractive
When light hits this type of crystal, the light will split into two parts and pass through it, with one part going straight through and the other part going through at an angle, so the two parts appear in two places, a small distance from each other, on the other side. In a sort of opposite way, if the crystal is above an image, two copies of the image a small distance apart will be visible through it. Calcite is the best known mineral for having this effect.
Doubly terminated
When a crystal has clean, sharp, naturally formed crystal faces (or “facets”) on both ends.
Druse
(see Druze)
Drusy
(see Druzy)
Druze
A layer of small crystals that usually give a rock a sparkly look.
Druzy
When a rock is coated with a layer of small crystals that usually give it a sparkly look. This can also be used to refer to the layer itself (see Druze).
E
Eon
One million years.
Etymology
The history of a word, including what language it comes from, what the original word was in that language, and what exact meaning the original word had.
F
Face
A perfectly flat naturally occurring surface on a crystal.
Facet
A perfectly flat surface of a jewel that is created by someone grinding and polishing a gemstone using lapidary equipment. Sometimes it’s used to refer to a perfectly flat, naturally occurring surface on a crystal, but technically that would be referred to as a crystal face.
Faceting
Making perfectly flat surfaces (see Facet) on a gemstone by grinding and polishing areas of it using lapidary equipment.
Feldspar
The most common mineral in the world, it’s a silicate that contains silicon (Si), aluminum (Al), and either potassium (K), sodium (Na), or calcium (Ca). Special varieties of feldspar include amazonite, labradorite, moonstone, sunstone, and others, but most feldspar is a plain whitish or pinkish mineral. When it breaks or cracks, it often does so into perfect rectangle shapes. Another special way to identify it is by “the feldspar flash”–if you find a piece and move it slowly in the sunlight, the whole surface of the piece will flash at you.
Field collecting
Going to localities and collecting minerals there in person, rather than buying them from stores, online, etc.
Floater crystal
A doubly terminated crystal that isn’t/wasn’t attached to anything inside the pocket where it formed (some Herkimer Diamonds for example).
Flow stone
A cave rock formation, usually made of mostly calcite, with a smooth surface. It can look like curtains, or flowing water, or melted-looking shapes.
Fluoresce
To react to ultraviolet (UV) light by glowing, often in a different color from what you see in normal light.
Fluorescent
Reacts to ultraviolet (UV) light by glowing, often in a different color from what you see in normal light.
Flux
A mineral added to metal or ore that is being melted while either refining it or using it to manufacture things with. It can help the metal/ore to melt more easily or be more liquid when it melts so it flows better. It can also help separate the metal that’s wanted from other minerals/metals that aren’t wanted.
Form
Depending on who you talk to and how specific they’re being, a mineral’s form may be considered the same thing as its crystal shape, a cube for example, or it may be the shape of just one face of a crystal, like a square that’s one face of the cube.
Fossil
An ancient plant or animal that has been turned into stone over thousands, millions, or billions of years.
Fossilized
Turned into stone.
G
Gem
A mineral that is valuable, is used to make jewelry, or both. Usually a gem is perfectly clear, has an attractive color, can be faceted, and is hard enough to handle daily use when included in a piece of jewelry.
Gemmy
Describes a crystal or a chunk of a mineral that is nice and clear, like a gem you’d find in a piece of jewelry.
Gemologist
A scientist who studies gemstones or a person who has specialized and detailed knowledge of gemstones and may be certified by a gemological institute.
Gemstone
(see Gem)
Geo
The name of the main character in the preeminent middle grade novel about rocks and magic, Geo’s Fortune. (see Geo’s Fortune)
The best middle grade novel about rocks and magic ever written, which everyone should go out and buy right now.
Geode
A pocket that is self-contained in its own personal rock. (see Pocket)
Geologist
A scientist who specializes in the study of the Earth, in terms of what it’s made of and the processes that form and affect the solid part of it, as opposed to the ocean or sky.
H
Habit
The overall shape of how a mineral commonly occurs. Although individual crystals of minerals may have a very standard shape, like a cube, some minerals usually only occur as groups of crystals in more complicated shapes. Habits can be those complicated shapes, but if a mineral usually just forms single crystals in standard shapes, that single crystal shape can also be considered the mineral’s habit (or one of its habits).
Hand specimen
A mineral specimen about 2 to 4 inches in size.
Herkimer Diamond:
A well-known example of often doubly terminated crystals from pockets that can be found all over the Herkimer County area in Upstate New York, not far from Albany. They are roughly football shaped, but with lots of crystal faces, and range in size from a sesame seed to, yes, a football…if you’re really lucky and have a jackhammer to get to them.
Hexagonal
Has a six-sided shape–think of a Stop sign—known as the most efficient shape in nature and commonly associated with different varieties of beryl, for example.
High grading
When you’re out somewhere collecting minerals, or as you add to your collection at home, you keep the better pieces of a mineral and get rid of the not so good pieces. Specifically, you start by picking up or purchasing any piece of the mineral, just so you have it, then if you find a better piece, you keep that and get rid of the worse piece.
Hydrothermal
Involving water and heat, this is one way minerals can form. Hot water from deep in the earth, or near or in magma or lava in volcanic areas, has dissolved minerals in it, and those minerals can be deposited and, if you’re lucky, form crystals when the water cools off or dries out.
I
Igneous
Rock that’s produced from magma, which is a bunch of melted together rocks and minerals in liquid form deep underground, or from lava, which is magma that is above ground, such as gushing out of a volcano.
Inclusion
A mineral that is found or occurs inside of another mineral, one of the more common inclusions being needle-like crystals of rutile inside of quartz crystals.
Index mineral
A mineral that tells you how much pressure and heat was present when the metamorphic rock the mineral is found in was forming. The pressure part usually refers to how deep in the Earth the rock was, whereas the heat can depend on how deep or on how close it was to a source of heat, such as a volcano.
Indicator mineral
A mineral that tells you something just by being where it is that you found it. It can “indicate” different types of things. One thing it can tell you is what other minerals you can expect to find in a place or a rock deposit where you found the mineral.
Iridescent
Coming from the Latin word for rainbow, it refers to that rainbow-like shininess you can see when, for example, oil or gas floats on water. The same Latin word is the source of “iris,” which is the colored part of our eyes.
J
Jewel
A gemstone, usually one that has been faceted.
K
Karst
A large area or landscape of limestone that often shows erosion and dissolving of parts of the stone by weakly acidic rain. The erosion can be of aboveground rock, such as mountains and exposed rock ledge, or of rock below ground, forming caves, underground rivers, and underground lakes. Or it can be in the form of sinkholes between the surface and underground. Of course, it can also be any two of those or all three.
Kimberlite
A roughly cylinder-shaped vertical deposit of volcanic rock that goes deep down into the Earth. A kimberlite is formed when a volcano erupts strongly and deeply, bringing materials up from far below the Earth’s surface, including diamonds that formed in the upper mantle. This type of rock is the best place to find diamonds.
L
Labrador-escence
Looking like labradorite, that is, having what look like shimmering layers of blue, green, silver, and other colors that seem to move inside of a mineral as you turn it or look at it from different directions.
Lamping
When you shine a UV light on a rock or mineral to see if it glows, which can help you see if there are any special minerals in or on it.
Lapidary
Related to grinding and polishing, or sometimes carving, rocks and minerals to create attractive pieces such as cabochons to include in jewelry. Sometimes a person who does lapidary work is also called “a lapidary.”
Lava
Totally melted together rocks and minerals in liquid form when it pours out onto the surface above ground, such as from a volcano. (see also Magma)
Leaverite
A piece of rock or mineral that you find but isn’t worth keeping—just “‘leave ’er right’ there.” (see also High grading)
Locality
A location, specifically one where a mineral or minerals can be found. Often this will be a mine or a quarry, but it can also be an outcropping of rock, a prospector’s pit, a mountain, a park open to rock collecting, etc.
Longwave UV light
A type of light, which you might think of as weaker than shortwave UV light, that will cause certain minerals to glow in certain colors. Often the glow will be a different color or will be less intense than the color you get if you use a shortwave UV light.
Loupe
A small magnifier with 5X or 10X power that you can hang on a strap or string around your neck or keep in your pocket and helps you see crystals more clearly and identify them.
Luminescent
When something glows by converting some kind of energy into light. The energy can be from light that shone on it, electricity, a chemical reaction, etc.
Luster
How shiny a mineral is, or exactly what kind of shininess, or lack of shininess, it shows. (see also Refractive index)
M
Magma
Totally melted together rocks and minerals in liquid form deep underground. (see also Lava)
Mantle
The middle layer of the Earth’s structure, between the crust and the core. It’s much thicker than the crust–1,800 miles(!), is mostly solid, and is mostly made of silicate minerals such as pyroxenes, olivine, and garnet.
Massive
When a mineral doesn’t form a crystal, has no faces, is opaque, and is in a chunk or shaped like a standard rock. And, you guessed it, rocks themselves are considered massive.
Matrix
On a mineral specimen, this is the mineral or rock that the more important, interesting, rare, or valuable mineral or crystal is attached to.
Medieval times
(see Middle Ages)
Metamorphic
Rock that is created when another type of rock is squeezed under a lot of pressure, heated, or both, causing the rock to change form (meta means “change” and “morph” means “shape” or “form”) to a different type of rock, often with minerals inside it changing as well or with new minerals forming.
Meteorite
A space rock that has hit the Earth (or some other planet).
Micro
(see Micromount)
Micrometeorite
A very tiny meteorite, less than 1 millimeter in size.
Micromount
Also called just a “micro,” it’s a mineral specimen about 1 millimeter (0.04 inches) to 1 inch (25.4 mm) in size. It’s smaller than a thumbnail. (see also Perky box)
Middle Ages
From about the year 500, after the fall of the Roman Empire, to sometime in the fifteenth century in Europe.
Mineral
A solid material that has a specific chemical formula and is made up of a certain amount of one or more elements.
Mineralization
The amount of minerals present in a deposit of rock. For example, the amount of rare earth elements or lithium in a pegmatite.
Mineralogist
A scientist who specializes in the study of minerals.
Mineraloid
A solid material that has a lot of the qualities and characteristics of a mineral but isn’t actually a mineral. Some examples would include amber, coal, and pearls.
Mineral rose
A mineral crystal habit that is made up of multiple crystals shaped like flower petals that together form a rose shape or shape that generally looks like a flower. Minerals such as baryte, gypsum, and hematite can crystallize in this habit. (see also Desert rose)
Mourning jewelry
Jewelry made using black rocks and minerals that was worn during the Victorian Era. Women whose husbands, children, or other family members had died would wear such jewelry, which was often made of jet, in memory of those who had passed on.
N
Native element
Minerals that can be only made up of themselves, or, more specifically, their element, such as gold, silver, and copper, without any other mineral or element mixed in.
Nodule
A rounded lump of a rock or mineral inside of a different kind of rock, for example, flint nodules inside of chalk deposits.
O
Opalescence
Looking like opal, that is, looking like a mineral that contains a sparkly kaleidoscope of color.
Opaque
Not letting any light pass through—no transparency or translucency; for example, massive minerals and most rocks.
Ore
Rock that includes a valuable mineral or minerals, usually a metal, but needs to be processed–crushed, heated until melting, etc.—to get the valuable mineral out, separating it from the nonvaluable stuff.
Oxide
A mineral that is made up of one or more elements combined with oxygen, with one of the most well-known oxide minerals being rust (iron oxide).
Oxidize
For our purposes, to react with oxygen in the air or in water or other substances to create an oxide mineral. This reaction can increase if you heat up a mineral as well.
P
Paleontologist
A scientist who studies ancient life by examining fossils. Widely considered to be among the coolest and best people on Earth. Hey wait, I think somone has commandeered the glossary!
Panning (for gold)
Using a pan to separate pieces of gold from dirt, sand, and other rocks and minerals. Originally the pan used to be a pie pan (used for baking pies), but today’s pans are larger and made especially for catching gold while the other stuff is washed away. Gold is heavier than almost everything else, so people swirl water in the pan to wash away the lighter material, and the gold sinks to the bottom of the pan and stays there.
Pegmatite
A type of rock in which the minerals that make it up–mainly feldspar, quartz, and mica with others—occur in larger crystal sizes than in most other types of rock. Pegmatite is known for having mineralization that allows for the formation of several types of gemstones. The word pegmatite can also refer to an individual deposit of this type of rock. For example, you can say “I have several pegmatites on my property.”
Percolate
To slowly trickle as a liquid down through a loosely packed solid. For geologists, it’s usually rainwater passing slowly down through soil and porous rock (rock that has holes in it). For coffee drinkers, it’s hot water passing slowly through ground-up coffee beans.
Periodic table
A chart that was originally created in 1869 with the goal of listing all the different elements (hydrogen, oxygen, sulfur, silicon, etc.) in an organized way. To keep the table from getting too big, each element’s name was shortened to one or two letters. For example, hydrogen became “H,” oxygen became “O,” sulfur became “S,” and silicon became “Si” (with the ‘i’ added so it wouldn’t get confused with sulfur).
Perky box
A small hinged plastic box with a black bottom and a clear top that you use to store a micromount in. Thumbnail-sized perky boxes are also available. (see also Micromount)
Petoskey stone
A type of fossil most often found on the shore of Lake Michigan that has hexagonal patterns in it and has often been worn down by the waves, so it’s shaped like other rocks. The fossil was originally a type of coral that lived about 350 million years ago.
Petrified
Turned into stone.
Phosphor-escent
When something absorbs light then emits it slowly, such as a glow in the dark frisbee or glow in the dark vampire teeth…oh yeah, or certain minerals.
Pipe
(see Kimberlite)
A hollow area inside of a large quantity of rock (a ledge, a wall of rock, the side of a mountain, the floor or wall of a quarry or mine) that allows crystals to grow out into the empty space without interference, hence allowing them to be larger and/or more perfect. (see also Vug)
Pseudomorph
When one mineral takes the shape of another mineral. This can happen a number of ways, but the two main ways would be by transforming or by, basically, filling a hole. An example of transforming would be how an azurite crystal can slowly change into malachite, so you end up with an all green crystal shaped like what would normally be an all blue azurite crystal. As for filling a hole, often pyrite will dissolve, since part of it can easily turn into sulfuric acid, then the iron mineral goethite will sneak into the hole that’s left behind and become a goethite crystal shaped like a pyrite crystal.
Pyroxene
A large group of silicate minerals that form under high pressure and/or temperature, such as in the Earth’s mantle. The group includes a lot of minerals you’ve never heard of, as well as diopside, jadeite, and spodumene.
R
Refractive index
A measure of how shiny a mineral is, used specifically by gemologists when looking at gemstones. Unlike luster, it can be measured with a scientific instrument, called a refractometer, and has a specific value, so you can use it to identify a mineral more accurately. (see also Luster)
Rock
A solid material that is made up of more than one mineral. Some people call all minerals rocks as well, especially if they collect both and want to make their lives easier when talking about them.
Rock cabinet
A display case, sometimes with a glass front and lights inside, where you keep and show off your rock collection.
Rockhound
A person who loves looking for rocks.
Rockhounding
Looking for rocks.
Rockhunting
Looking for rocks.
Rutilated
When a mineral contains usually needle-shaped crystals of rutile, the most common being rutilated quartz.
S
Schiller
Also called the Schiller Effect, a way that certain minerals react to light that produces a shimmering, changing color, or glowing appearance. Several of the “-escences” are considered types of Schiller effects. (see “The Essence of “‑escence”” in “The Science Behind Rocks and Minerals”)
Secondary mineral
A mineral that forms when another mineral (the “primary mineral”) breaks down, for example by oxidizing, creating a new mineral or minerals that have different formulas from the original mineral. For example, azurite and malachite are secondary minerals that form when the mineral copper oxidizes, often with the help of any sulfur that might be in the copper ore, which can form sulfuric acid.
Sediment
Small particles of mud, dirt, sand, or shells or skeletons of sea creatures.
Sedimentary
Rock that’s created when layers of sediment are compressed by the weight of other layers of sediment, or of other types of rock, on top of them, and solidify.
Serpentin-ization
The metamorphic process that causes iron and magnesium minerals along with a lot of water to be transformed into serpentine minerals, including asbestos, lizardite, antigorite, talc, and others. Depending on how much heat, how much pressure, and how much of specific elements are in the original minerals, different serpentine minerals will form, all together in big masses.
Shape
The way a single crystal of a mineral ends up looking when it forms, in terms of how many sides it has, how big different sides are compared to others, what the angles are between the sides, etc. Scientists call this the mineral’s crystal system. What we’d call a cube shape, some scientists call the cubic system, while others call it the isometric system.
Shortwave UV light
A type of light, which you might think of as stronger than longwave UV light, that will cause certain minerals to glow in certain colors. Often the glow will be a different color or will be more intense than the color you get if you use a longwave UV light.
Silicate
A mineral that has silicon in its formula, often in the form of SiO4, which is silicon and oxygen combined. Feldspar and quartz are the most common examples, but there are many more.
Sill
A deposit of rock that fills a crack–or makes a crack then fills it–between layers in a larger rock deposit. (see also Dike)
Silver pick collecting
Collecting rocks by buying them rather than field collecting. The silver part refers to the fact that many coins used to be made of silver. So a “silver pick” is money, compared to a steel pick, which is a tool you’d use to dig minerals out of a rock or the ground.
Smelting
The process of melting ore and combining it with specific industrial chemicals or minerals to get pure metal, such as iron, lead, or copper, out of the ore.
Specific gravity
For our purposes, how dense a mineral is if you compare it to water. This is related to weight, but is more, well, specific. Each mineral tends to have a special specific gravity, so you can use its specific gravity to help you identify the mineral if you don’t know what it is.
Spectrum
A range of colors. A rainbow is one example of a spectrum, but spectra (the plural of spectrum) can have just a few colors or even more colors. The rainbow (spectrum) of different colors in sunlight, which you can see when you put a prism in the light, is very useful for mineral collectors because at one end it includes ultraviolet (UV) light, and you can use UV light to help identify minerals.
Stalactite
A rock formation that grows down from the ceiling of a cave, as drops of water with dissolved minerals in them drip from the ceiling, depositing tiny amounts of minerals as they flow downwards, before they evaporate or the water drops to the floor. A stalactite can be straight like a straw or wider at the ceiling and narrow to a point at the bottom, like an icicle. To remember the difference between stalactites and stalagmites, remember that stalactites hang “tite” to the ceiling. (see also Stalagmite)
Stalagmite
A rock formation that grows from the floor of a cave, as drops of water with dissolved minerals in them drip from the ceiling, depositing tiny amounts of minerals when they hit the floor. The minerals very slowly, microscopically, pile up, building formations shaped like icicles or carrots, with the more pointy part sticking up. To remember the difference between stalagmites and stalactites, remember that you have to be careful walking around stalagmites because they stick up from the ground, and you “mite” trip and impale yourself on one of them. (see also Stalactite)
STEM
An acronym for science, technology, engineering, and mathematics.
Sulfide
A mineral that’s made up of one or more elements combined with sulfur, with one of the most well-known sulfide minerals being galena (lead sulfide).
Synthetic
Created by people using special chemistry and/or machinery, along with heat, pressure, and/or radiation. Rubies, topaz, diamonds, and other gemstones can be created this way, and they will have the same exact formula and look exactly the same overall as the natural gemstones, but they won’t have the natural impurities that the real gemstones have.
T
Tabular
A crystal form that’s pretty flat, like a table, such as “window pane” wulfenite crystals.
Tectonic plate
An extremely large (wide) mass of rock that’s beneath a large area of land and/or ocean. And by large, we mean it can be as large as a continent, thousands of miles wide. Tectonic plates move around, extremely slowly, and can run into each other, and over millions of years they can create mountain ranges where they meet.
Tenebrescent
When a mineral can lose its color in sunlight but then get it back if it’s left in the dark for a while or exposed to ultraviolet light. Hackmanite, a variety of sodalite, is the mineral most well known for this effect.
Terminated
When a crystal has a clean, sharp, naturally formed crystal face (“facet”) on the end.
Termination
The end or top of a crystal.
Thumbnail
An approximately thumbnail-sized mineral specimen, about an inch or two in size.
Toenail:
A mineral specimen on the larger end of a thumbnail size. (see Thumbnail)
Tourmaline
A group of minerals that have very complicated formulas and include schorl, dravite, uvite, all the different kinds of elbaite, and others, but if someone says “tourmaline,” they usually mean the colorful kinds that are elbaite.
Translucent
Allows light to pass through it, such as amethyst.
Transparent
Allows both light and images to pass through it, such as window glass.
Trap rock
Hard igneous rock, such as basalt or diabase, the largest example on Earth being the Deccan Traps in India. Named after the Swedish word for “stairs,” since different layers of the rock can break off in chunks, leaving a staircase shape.
Type locality
The place where a mineral was originally discovered. For minerals discovered in recent times, this often refers specifically to where someone found a mineral that was then tested using scientific instruments to confirm its identity as being found there first before anywhere else.
U
Ultraviolet light
(see UV light)
UV light
A special electric- or battery-powered device, such as a lamp or a flashlight, that emits light that makes certain minerals glow in certain colors because of how they react to it. It also can refer to the kind of light that comes out of the device–similar to the beam of light from a flashlight.
V
Victorian Era
The years from 1837 to 1901, when Victoria was the Queen of England.
Vug
A very small pocket, a quarter inch to a couple of inches deep. (see Pocket)
Vuggy
How you’d describe a deposit of rock, or an individual rock, that has a number of vugs in it.
Y
Yard rock
A rock or mineral specimen that’s too large to keep in your rock cabinet and usually isn’t very valuable but looks nice in your yard or garden.
Yooperlite
A rock found along Lake Superior that glows bright orange, like a hot ember in a fire, when you shine a UV light on it. The mineral sodalite in the rock is what reacts to the UV light. The rock’s name comes from the nickname “Yooper,” which means a person from the part of Michigan called the Upper Peninsula.
Z
Zones
Layers or areas of a crystal that form with different colors or shades of color, or even a different mineral inside the crystal, as the crystal grows.