Are Emeralds Real?

“Dad?” my son said from the back seat of the car. “Are emeralds real?”

Mercifully, there is some context for that question. He’d been over at a friend’s house, and they’d been playing Minecraft. I don’t know much about the game, but apparently “emerald” is one of the construction materials in the game. Which led to the question.

“Yes,” I tell him. “They are.”

“Wow!” he says.

You knew this one, didn’t you?

Yes. Yes I did. But let’s have some fun with it anyway, because I don’t know as much about them as I’d like.

What is an emerald?

Every source I found (which includes mindat.org, minerals.net, and Wikipedia agree that emerald is a variety of beryl. Chemically it’s beryllium aluminum silicate (Be3Al2Si6O18), with a green color that derives from trace amounts of chromium (the mineral that gives us chrome) and (occasionally) vanadium (a silvery grey mineral). Both minerals oxidize in a variety of colors, which explains how a silvery mineral can turn the mineral green. It naturally forms into hexagonal crystals.

The full market value of an emerald is based on four factors: color, clarity, cut, and carat weight.

  • Color: To be an emerald, the mineral must have a medium to dark green color (light green stones are classified as “Green Beryl“, which is not considered as valuable), as measured on a scale from 0% (colorless) to 100% (opaque and black) – the finest emeralds rank about 75% on this scale.
  • Clarity: All crystals will have some level of flaws, mostly consisting of inclusions (other minerals trapped in the crystal) and cracks. Flawlessly emeralds are stones with no inclusions or fissures visible to the naked eye.
  • Cut: This is not a natural property of the stone, but the way it was cut after it was mined. Raw stones are less valuable for the same reason that a tree trunk sells for less per pound than a table of the same wood, but a bad cut can destroy the stone.
  • Carat weight. A carat is 0.2 grams (or 0.007055 oz). The value of stones of th same quality does not change in a linear fashion, because larger high-quality stones are rarer than smaller ones. Consulting Singhal Gems International, a good quality 1.0 carat emerald can range from $500 to $1,125, while a good quality 5.0 carat emerald can range from $7,500 to $15,000 in value.

Where are they found?

The largest emerald deposits can be found in Colombia, Brazil, and Zambia. They are mined elsewhere in the world, but those three nations produce most of them. Colombian emeralds are often considered to be the overall finest form of emerald, as they are primarily colored by chromium. Zambian and Brazilian emeralds are more frequently colored by vanadium, with Brazilian emeralds being darker and more heavily included and Zambian emeralds having a bluish-green or grayish-green color.

What is the biggest emerald ever found?

That’s… tricky. What, exactly, do you mean by that question?

The International Gem Society website breaks them down into three categories: named emeralds, unnamed emeralds, and “other large emeralds”. They state that the largest named emerald is the “Emerald Unguentarium”, a 2,860 carat emerald vase currently on display in the Imperial Treasury in Vienna.

The Daily Mail disagrees with this statement, as they report on a watermelon-sized emerald named Teodora, which came in at 57,500 carats. It should be noted, however, that gem experts were skeptical of this claim, and that the owner was arrested on multiple fraud charges. A gem expert who studied it found evidence that it was lower-quality emerald (possibly mixed with white beryl) that had been dyed to make it appear more valuable. Because of this, when it went up for auction, no bids were made.

The largest unnamed emerald is an uncut Colombian crystal in a private collection that weighs 7,052 carats.

“Other large emeralds” is dominated by the Bahia Emerald, which was an 840 pound stone from Bahia, Brazil. The stone “reportedly contains over 180,000 carats of emeralds”, one of which is a single stone that is apparently described as the size of a man’s thigh. There is an ongoing legal battle over ownership of this stone, which shouldn’t surprise anyone since it’s been valued at upwards of $400 million. This stone, unlike Teodora, appears to be genuine.

Genuine, and large.

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Can Metal Turn Into Fire?

The three of us – me, my wife, and my son – are on our way home from dinner yesterday, and my son’s been talking excitedly about a video game he got to play in a store.  “And then I knocked him into the water,” he announces, “and then I knocked him into the air, and then I won!  Daddy didn’t win a lot, though.”

“I made the mistake of trying to figure out what the buttons do,” I add.  “Our son just pushed things at random.  It’s nice to see that button-mashing is still a strategy.”

“Can metal turn into fire?” my son asks.

Eh?  Where did that come from?  My wife and I look at each other quizzically.  “It can melt,” she says, slowly.

“But can it turn into fire?”

“Do you mean ‘can it burn?'” I ask.

“Yeah!”

“I… think so?”

Can metal burn?

Brief answer: Yes. And in different colors.

Like I told my son, I think so.  Long ago, I was told that burning is just a special form of oxidation (aka “rusting”).  I don’t remember who told me that, or when, or why, so I don’t know that I can trust it.  Also, I vaguely recall that thermite is a metal that burns, and that titanium can burn.  So, yeah.  I’m utterly ignorant on the subject.

Let’s start with “burning”.

Conveniently, a while back I wrote an article titled “When Ice Is On Fire, Does The Ice Melt” where I discussed the concept of burning.  Here’s what I wrote:

Burning, more properly called a combustion reaction, is a little more complicated. There’s an entire subfield of chemistry called thermochemistry that deals with burning (or, more properly, the energy release from a combustion reaction). In general, though, you need a compound to combust and an oxidant to react with the combusting compound, and some energy to get it started. The oxidant and the combusting compound then combine in a chemical reaction to produce one or more new compounds, and since the reaction is exothermic the process of making the new compound(s) generates more energy than it gives off.

Yes, that does mean that once you get a combustion reaction started it will continue as long as it has combustible compounds and oxidants. That’s why fire spreads.

It turns out that I’d missed two important concepts when I wrote that article, though:  flash point and ignition temperature.  The flash point is the lowest temperature at which a combustable substance vaporizes into an ignitable gas, while the ignition temperature is the lowest point at which a combustable substance vaporizes into a gas that will self-ignite.  Note that word “combustable”, though.  Not every substance has a flash point or ignition temperature, because some substances (such as water and other combustion reaction products) are simply not combustable.

Look, we’ve been patient.  Can metal burn?

Well, some can.  If they’re combustible, which gets to the best definition I’ve seen in a long time:  “A combustible metal is defined as any metal composed of distinct particles or pieces, regardless of shape, size or chemical composition that will burn.”  Literally, a metal is defined as a metal that can burn if it is a metal that burns.  Although, in fairness, “burns” means “sustains ignition”.

The combustible metals that are :

And because I know you’re curious, here’s some sample solid metal ignition temperatures.  Bear in mind that, for comparison purposes, a Bic lighter can reach temperatures of 3,590.6 F (1,997 C):

  • Aluminum:  1,832 F (555 C)
  • Barium:  347 F (175 C)
  • Calcium: 1,300 F (704 C)
  • Iron: 1,706 F (930 C)
  • Lithium: 356 F (180 C)
  • Magnesium: 1,153 F (623 C)
  • Plutonium: 1,112 F (600 C)
  • Potassium: 156 F (69 C)
  • Sodium: 239 F (115 C)
  • Strontium: 1,328 F (720 C)
  • Thorium: 932 F (500 C)
  • Titanium: 2,900 F (1,593 C)
  • Uranium: 6,900 F (3,815 C)
  • Zinc: 1,652 F (900 C)
  • Zirconium: 2,552 F (1,400 C)

Hang on.  I have so many questions now.

Yeah, probably.  Let me anticipate them.

A metal doesn’t have to be a “combustible metal” to burn.  Any number of other metals will burn as well, but only as long as you apply heat.  Combustible metals, however, sustain burning even after the outside heat source is removed.  Aluminum will burn like a log, but copper will only burn as long as you apply sufficient heat.

Your pocket lighter will probably not set your cast iron skillet on fire, for the same reason that it will not set a log on fire.  A significant percentage of the object that you are trying to burn has to be heated to the flash point before it will catch fire.  You could probably set a super-thin iron wire on fire with a lighter, but you’d need a larger and sustained flame to ignite something big.

 

Oh, and here’s two more useful facts to know:

  • “Burning combustible metals can extract water from concrete, intensifying burning to cause spalling and explosion of the concrete.”
  • “Water applied to alkali metals will result in hazardous decomposition, ignition or explosion.  Alkali metals include lithium, sodium, potassium, cesium and francium.”

So, if you do manage to set your cheap fake diamond on fire?  Call a professional.

 

What Are Crystals Made Of?

It’s summer, and my son and I are walking home from preschoool and he’s exploring the area and looking at everything. As he does, he stops at a smallish boulder that’s been left at the corner of a road by a landscaper. “Daddy!” he calls, “Look!” So I go and look. He’s pointing at a band of what I think is quartz, rippling through the stone. “What is that?”

“Those are crystals,” I tell him. “Like the ones we saw at the museum. Remember them?” We’d just recently been to the Cincinnati Natural History Museum, and one thing they had on display was a collection of different crystals and geodes.

“Oh,” he says, staring at the rock. “They’re pretty.”

“Yes,” I agree, “they are.”

“What are they made of?”

Uhm…

What is a crystal?

To begin with, let’s hit Merriam-Webster up. They define ‘crystal‘ as:

  1. quartz that is transparent or nearly so and that is either colorless or only slightly tinged
  2. something resembling crystal in transparency and colorlessness
  3. a body that is formed by the solidification of a chemical element, a compound, or a mixture and has a regularly repeating internal arrangement of its atoms and often external plane faces
  4. a clear colorless glass of superior quality; also : objects or ware of such glass
  5. the glass or transparent plastic cover over a watch or clock dial
  6. a crystalline material used in electronics as a frequency-determining element or for rectification

What is a Crystal, a page on University of California Berkeley’s College of Natural Resources site, says:

Something is crystalline if the atoms or ions that compose it are arranged in a regular way (i.e, a crystal has internal order due to the periodic arrangement of atoms in three dimensions).  Gems are described as amorphous if they are non-crystalline.

Crystals characterized by well developed crystal faces (external surfaces) are described as euhedral . Crystals do not always show well developed crystal faces seen on euhedral examples.

A crystal is built up by arranging atoms and groups of atoms in regular patterns, for example at the corners of a cube or rectangular prism.

The basic arrangement of atoms that describes the crystal structure is identified. This is termed the unit cell.

Crystals must be charge balanced.  This means that the amount of negative charge must be compensated by the same amount of positive charge.

 

So what are crystals made of?

Atoms.

More usefully, Crystal Structure of the elements says that the only elements that don’t form crystals are promethium, astatine, radon, francium, einsteinium, fermium, mendelevium, nobelium, lawrencium, rutherfordium, dubnium, seaborgium, bohriumhassium, meitnerium, darmstadtium, roentgenium, unubium, unutrium, unuquadium, ununpentium, ununhexium, ununseptium, and ununoctium. Of all of these, only radon is found naturally on Earth, and the idea that it has no crystal structure is contradicted by Elements Database which states it has a cubic crystal structure. So it’s quite possible that the others have them as well, and we just don’t know because they tend to fall apart before we can see what they do.

The most common crystals on Earth tend to be made out of the most common elements on Earth. Why? Because they’re available to make crystals. These elements are oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg) in the proportions seen below.

I’ll be honest here, and say that I expected carbon (C) to be much higher on that list. You know, what with it being so vital to every living thing we see. But no. Carbon is part of the 1.5% “other”, and makes up only 0.15% of the Earth’s crust. Go figure.

Most likely, the crystal that caught my son’s eye was either feldspar or quartz – the boulder was granite, after all, and granite is largely made up of those two crystals. Quartz is silicon dioxide (SiO2), it comes in a variety of colors depending on the impurities in the crystalline structure, and it ranges from transparent to opaque. Feldspar is actually a group of three related minerals (KAlSi3O8, NaAlSi3O8, and CaAl2Si3O8) which can resemble quartz. I’m certain a minerologist could figure out the difference, but I certainly couldn’t. Not from a purely visual inspection, anyway.

What Is Glass?

My son and I were in my car when this happened. I was on my way to get an estimate on some body work for my car, and this got my son interested in things about the car. That combined with his interest in ice and cold, and he starts telling me about ice. “And then they melt the ice, and you can see through it!” he announces, because they’d been looking at ice. Then he asks, “how do they make the ice into windows?”

“They don’t,” I tell him. “Windows are made of glass.”

“Glass is made of ice!” he tells me. I… guess it makes sense? Glass and ice can look very similar, after all.

“No,” I tell him. “Glass is made of sand.”

He laughs at me. “No it’s not!”

“Yes, it is.”

“Then,” he asks, with the air of a prosecutor delivering the final damning bit of evidence, “how do you see through it?”

It’s a good question, really. The idea that sand – something he’s seen a lot of and [i]knows[/i] is opaque – can be seen through is really absurd sounding. I don’t have a good answer for that, really.

What is glass?

float-glass

Dictionary.com defines glass as:

noun

  1. a hard, brittle, noncrystalline, more or less transparent substance produced by fusion, usually consisting of mutually dissolved silica and silicates that also contain soda and lime, as in the ordinary variety used for windows and bottles.
  2. any artificial or natural substance having similar properties and composition, as fused borax, obsidian, or the like.

The Corning Museum of Glass offers this definition instead:

Glass is a rigid material formed by heating a mixture of dry materials to a viscous state, then cooling the ingredients fast enough to prevent a regular crystalline structure. As the glass cools, the atoms become locked in a disordered state like a liquid before they can form into the perfect crystal arrangement of a solid. Being neither a liquid nor a solid, but sharing the qualities of both, glass is its own state of matter.

Intuitively, I think most of us know what glass is. We interact with it all the time, in the form of windows if nothing else. Our everyday experience of glass tells us that it is hard (but obviously not indestructible, particularly when thin) and transparent.

How is glass made?

British Glass has a page titled All About Glass, which provides a general description of how glass is made:

Glass is made by melting together several minerals at very high temperatures. Silica in the form of sand is the main ingredient and this is combined with soda ash and limestone and melted in a furnace at temperatures of 1700°C. Other materials can be added to produce different colours or properties. Glass can also be coated, heat-treated, engraved or decorated. Whilst still molten, glass can be manipulated to form packaging, car windscreens, glazing or numerous other products. Depending on the end use, the composition of the glass and the rate at which it is allowed to cool will vary, as these two factors are crucial in obtaining the properties the glassmaker is seeking to achieve.

So, in other words, you melt sand with other stuff. Going back to the Corning Museum of Glass, they explain that “typical glass contains formers, fluxes, and stabilizers.” A former is the thing the glass is made of (silicon dioxide, aka silica, in standard windows and bottles). A flux is something that lowers the melting temperature of the former – soda ash (sodium carbonate) is a flux, as is potash (potassium carbonate). A stabilizer is something that makes the glass stronger (and often water resistant) – limestone (a form of calcium carbonate) is a stabilizer.

Interestingly, the page also states that without the stabilizer water will dissolve glass. Put this firmly into the category of Things I REALLY Didn’t Know.

Window glass is generally 73.6% silica, 16% soda ash, 5.2% limestone, 0.6% potash, and 4.6% other materials. By contrast, your glass baking dish is 80% silica, 4% soda ash, 0.4% potash, 2% alumina, and 13% boric oxide. Your fine lead crystal is 35% silica, 7.2% potash, and 58% lead oxide.

Why can we see through it?

Because it’s transparent.

No, really.

No, seriously. Transparent Glass doesn’t absorb photons of light in the visible spectrum. A glass like volcanic obsidian, on the other hand, does. In fact, it absorbs nearly all the light in the visible spectrum, which is why it looks black.

Could you be more specific?

I’ll try. Let me warn you in advance that I’m leaning heavily on Transparency and translucency from Wikipedia for this.

Any given wavelength of electromagnetic energy will be either reflected, absorbed, or transmitted by a given material. The human eye interprets reflected (visible) wavelengths as color, radar dishes and detect reflected radio waves to calculate distance and direction, and so on. Absorbed wavelengths increase the temperature of the material, because they’re pumping energy into the material. Transmitted wavelengths pass through unhindered to a greater or lesser degree. A material that transmits no portion of the visible electromagnetic spectrum is optically opaque, and a material that transmits all of the visible spectrum is optically transparent. Here’s a good quote from the article:

The atoms that bind together to make the molecules of any particular substance contain a number of electrons (given by the atomic number Z in the periodic chart). Recall that all light waves are electromagnetic in origin. Thus they are affected strongly when coming into contact with negatively charged electrons in matter. When photons (individual packets of light energy) come in contact with the valence electrons of atom, one of several things can and will occur:

  • A molecule absorbs the photon, some of the energy may be lost via luminescence, fluorescence and phosphorescence.
  • A molecule absorbs the photon which results in reflection or scattering.
  • A molecule cannot absorb the energy of the photon and the photon continues on its path. This results in transmission (provided no other absorption mechanisms are active).

Most of the time, it is a combination of the above that happens to the light that hits an object. The states in different materials vary in the range of energy that they can absorb. Most glasses, for example, block ultraviolet (UV) light. What happens is the electrons in the glass absorb the energy of the photons in the UV range while ignoring the weaker energy of photons in the visible light spectrum. But there are also existing special glass types, like special types of borosilicate glass or quartz that are UV-permeable and thus allow a high transmission of ultra violet light.

Interestingly enough, when I first wrote this out I wrote the following statement: “a material that transmits some portion is optically translucent to a greater or lesser degree”. This is actually incorrect. Optically translucent objects are considered optically transparent, but there is a quality to the material that prevents image formation. That is, visible light will pass through but it is scattered in such a way that you can’t make out what the source image on the other side is.

So. Glass is transparent because the molecules that make up the glass literally cannot absorb most of the electromagnetic energy in the visible spectrum (although it can reflect it, which is why you can sometimes see yourself in glass).

Is it a solid or a liquid?

You hear quite often that glass is a really slow-moving liquid. It isn’t. Glass is an amorphous solid, and to understand what that means we’ll need to explain what a crystalline solid is first.

Please do.

A crystalline solid is also called a crystal, and it is a solid where the atoms or molecules that make up the substance are arranged in a highly organized and periodic structure. Think of the atoms or molecules as the bricks in a brick wall or Lego structure. Individual crystalline solids can get really, really big.

crystal-cave-of-the-giants
A real picture, from the Naica Crystal Cave

Most solid objects are polycrystalline, meaning they are made up of multiple crystals. Each crystal can be arranged in a haphazard fashion relative to the other crystals – imagine taking that Lego structure above, breaking it into chunks, and then covering those chunks with glue and tossing them in a box. (Clearly, this analogy breaks down quickly. Just bear in mind that we’re imagining structures here, not chemical properties.)

Amorphous solids have no organization to the component atoms or molecules. Using the Lego analogy, they’re a sack full of individual Lego bricks (that were all coated with glue). They’re still solids – the individual atoms still have strong connectivity – but they have some liquid-like properties. They can flow, slightly, as the disorganized components try to arrange themselves into crystalline structures. As the Scientific American article I linked to notes, though, this is not why some antique glass looks thicker at the bottom. “[A]ncient Egyptian vessels have none of this sagging, says Robert Brill, an antique glass researcher at the Corning Museum of Glass in Corning, N.Y. Furthermore, cathedral glass should not flow because it is hundreds of degrees below its glass-transition temperature, Ediger adds. A mathematical model shows it would take longer than the universe has existed for room temperature cathedral glass to rearrange itself to appear melted.”

What Is The Softest Thing Ever?

Recently, I was helping my son put his bed back together – a labor-intensive process involving fleece blankets. He has something like eight or ten of them, all of which he insists on sleeping under when we put him to bed, so most of them end up on the floor because he gets hot and kicks them off. No big deal, really. It’s hardly the worst sleeping habit he could have.

“Now, the big one next,” I tell him, spreading his quilt on the bed.

“Yes,” he agrees. “It’ll make my bed [i]so soft[/i]!” Then he thinks about that as he hands me his Darth Vader fleece blanket. “What’s the softest thing ever?”

You know what? I have no idea.

Hardness versus Softness

“Hard” and “soft” are words that we use with some regularity. Most of us have an intuitive understanding of the meaning, even if we can’t define it with precision. But, in order to further our discussion of the subject, we should get a formal definition of each. Or, at least, that sounds reasonable. The problem is, Dictionary.com has 41 different definitions for the word hard and 38 for soft. The first definition of “hard” is “not soft; solid and firm to the touch; unyielding to pressure and impenetrable or almost impenetrable.” By comparison, “soft” is defined as “yielding readily to touch or pressure; easily penetrated, divided, or changed in shape; not hard or stiff.”

So, by definition, soft things are not hard and hard things are not soft. Thank you, Dictionary.com.  Fortunately, the University of Maryland provides a more technical definition of hardness:

The Metals Handbook defines hardness as “Resistance of metal to plastic deformation, usually by indentation. However, the term may also refer to stiffness or temper, or to resistance to scratching, abrasion, or cutting. It is the property of a metal, which gives it the ability to resist being permanently, deformed (bent, broken, or have its shape changed), when a load is applied. The greater the hardness of the metal, the greater resistance it has to deformation.

In mineralogy the property of matter commonly described as the resistance of a substance to being scratched by another substance. In metallurgy hardness is defined as the ability of a material to resist plastic deformation.

The dictionary of Metallurgy defines the indentation hardness as the resistance of a material to indentation. This is the usual type of hardness test, in which a pointed or rounded indenter is pressed into a surface under a substantially static load.

So, in brief, hardness is the ability of a substance to resist being permanently deformed or scratched.

How Do You Measure Hardness?

Sometimes, you just have to turn to Wikipedia: “There are three main types of hardness measurements: scratch, indentation, and rebound. Within each of these classes of measurement there are individual measurement scales. For practical reasons conversion tables are used to convert between one scale and another.”

Scratch hardness is generally measured with a sclerometer, a device that measures “the width of a scratch made by a diamond under a fixed load, and drawn across the face of the specimen under fixed conditions”.

AGY_Series_Fruit_Sclerometer
A sclerometer

Indentation hardness is primarily used in engineering and metallurgy, and measures “the resistance of a sample to material deformation due to a constant compression load from a sharp object”. Regardless of the specific test used (and there are several), the test uses a dense object of spherical or conical shape, pushed into the material under a specific pressure for a specified period of time. The depth of the resulting indentation is then used to determine how hard the material is.

Rebound hardness “measures the height of the “bounce” of a diamond-tipped hammer dropped from a fixed height onto a material”. The actual device with the hammer is called a scleroscope.

The Softest Thing Ever? How About The Hardest?

Since there isn’t a standardized definition of hard or soft, can we actually talk about the “hardest’ or “softest” thing? The answer is “sort of”. For example, diamonds are able to survive pressures of around 150 GPa. GPa is the scientific notation for “gigapascals”, where one pascal is helpfully defined as the pressure exerted by a force of magnitude one newton perpendicularly upon an area of one square meter (or, if this makes more sense, one kilogram of mass over one square meter for one second). For comparison purposes, one atmosphere of pressure is 101.325 kilopascal (kPa) – which is .000101325 GPa.

In other words, natural diamonds can withstand approximately 1,480,000 times the pressure of Earth’s atmosphere at sea level. Impressive, right? Well, yes. Yes it is. But researchers in the Technological institute for Superhard and Novel Carbon Materials and the Moscow Institute of Physics and Technology have developed a new method of synthesizing ultrahard fullerines, which can withstand upwards of 300 GPa – although the process is not yet ready for industrial scales. Why? Well, making the ultrahard fullerite requires pressures in excess of 13 GPa – the article states that “modern equipment cannot provide such pressure on a large scale.”

Fullerene_C60
The ultrahard fullerine molecule

Looking at a different measure of hardness, neutron degenerate matter (aka the stuff neutron stars are made out of) is theorized to have a Young modulus that is 20 orders of magnitude larger than that of diamond. So, by at least one measure of hardness, that is the hardest thing known.

Softness is trickier. The softest possible thing would be a material with no resistance to deformation or scratching. You could argue that a vacuum has none of those resistances, but then you could also argue that vacuum is – by definition – not a material. Maybe whipped cream, or soap suds? Honestly, just like you get arguments about how hard something is based on the test applied, you’d probably get similar arguments for how soft something is.

159706-357x421-kitten

So I’m declaring kittens the softest thing ever. Try to prove me wrong.