ROOTSHUNT

Presuming you want the most gold possible would you rather have a Troy ounce of gold or an English ounce? or Would you rather have a Troy pound of gold or an English pound of gold?.

Troy ounce. If we use carats, then it's easy to decide on the Troy ounce which weighs 156 ct. compared to the English ounce's 142 ct.

English pound. Since there are only 12 Troy ounces in a Troy pound, then there are only 12 x 156 or 1872 carats in a Troy pound, whereas there are 16 x 142 = 2272 carats in an English pound, as English pounds have 16 ounces each.

Suppose you're a budding gem cutter or collector, and you happen to be at a swapmeet where a vendor has some transparent pink gem rough to sell. He knows that it is either Kunzite (pink spodumene) or pink tourmaline, but just can't remember which one. You have been wanting some pink tourmaline, so you look at the material closely and can't find any evidence of cleavages, even using your 10 power magnifier. Of the two choices, which is it most likely to be?

It is probably pink tourmaline, as tourmaline has no cleavage and Kunzite has two perfect cleavages.

A big decision is coming up in your life you are about to choose an engagement ring. Not being a slave to tradition, you are considering a colored stone for the piece, rather than a diamond. You want a blue stone, and your top contenders are: blue topaz, and blue sapphire. Considering that engagement rings are worn all day, every day, for many years, you do not want a stone that is likely suffer a cleaveage that will crack or break it. Which is your best choice?

You should choose the blue sapphire. Sapphire has no cleavage and blue topaz has perfect leavage in one direction.

You've found a beautiful piece of apatite rough and want to have a stone cut from it. You approach your friend who is a facetor, and ask him/her to cut you a marquis shaped stone from the piece. The cutter declines and says they will cut an oval or round but not a marquis. Why?

Very thin or pointed areas on a cut gem, like the tips of a marquis cut, are areas of weakness; since apatite has cleavage, it would be much safer in a shape with smooth curves like a round or oval.

When the sellers of Moissanite send their pieces of rough to be cut, they are very careful to mark the optic axis direction on each piece. Why?

Seeing a conchoidal fracture pattern on the edge of the broken piece would indicate that is not turquoise (or coral) whose fractures are granular and uneven, respectively, but it could very well be glass.

Suppose we had a 6 mm round calcite, and a 6 mm round Smithsonite, cut to the same proportions Which would be heavier? Or to turn it around, if we had a one carat round calcite and a one carat round Smithsonite, which would be bigger?

The 6 mm Smithsonite is quite a bit heavier than the same sized calcite. The one carat calcite is noticeably larger than the same weight Smithsonite.

Suppose we had a 6 mm round calcite, and a 6 mm round aragonite, cut to the same proportions Which would be heavier? Or to turn it around, if we had a one carat round calcite and a one round carat aragonite: which would be bigger?

The 6 mm aragonite is a bit heavier than the same sized calcite. The one carat calcite is slightly larger than the same weight aragonite.

Look up the SGs for gold and platinum in the back of the Hall text. (Even if platinum sold for the same price as gold, which it doesn't) why would it cost more to make a particular size and type of ring in platinum than in gold?

Even if gold and platinum were equally priced per ounce, the amount of platinum required for a given size and shape ring would weigh more (because it is denser) making the platinum ring more expensive.

When the sellers of Moissanite send their pieces of rough to be cut, they are very careful to mark the optic axis direction on each piece. Why?

They mark the optic axis direction so that the cutter can be sure to orient the table of the stone in the proper direction. When a Moissanite is cut with the table in the optic axis direction, its birefringence isn't noticeable, and it looks more like a diamond.

Your friend shows you his new "diamond" ring. You look down through the table and you see no doubled facets. You take out your loupe (magnifier) and turn the gem at an angle so that you are not viewing straight through the table, and when you look at the stone, you see doubled images of all the facets. Could this be a diamond? Could it be a Moissanite?

The table view looks as if the stone is SR. When you tilt the stone you are looking throught in a non-optic axis direction, and in this case you see doubled facets indicating that has birefringence and therefore is DR. Since diamond is SR, and the stone is DR, it cannot be a diamond. Moissanite, used as a diamond simulant is DR, so the gem could be a Moissanite. Another possibility would be a white zircon, a natural stone used as a diamond simulant which is also DR.

You have three blue transparent gems: an iolite, a spinel, and a sapphire, but they have no labels on them. Can you find the spinel? Can you separate the iolite from the sapphire? How?

Yes, by testing the three gems with the dichroscope you would find the one which shows no pleochroism which would be the spinel which is SR. The other two would have pleochroism. You could compare the other two to separate them: iolite is trichoic so you'd see three colors, sapphire is dichroic showing only two.

You have three red transparent gems, also without labels: a piece of glass, a ruby and a garnet. Can you find the ruby? Can you separate the glass from the garnet with your dichroscope?

Yes, the ruby would be the one that was dichroic. The other two, being SR gems wouldn't how pleochroism. No, using just the dichroscope and no other test or information you could not separate the garnet and the glass. (testing for RI or specific gravity would easily separate them, though.)

You have three transparent, red pieces of gem rough, (again, no labels): one is a ruby, one a garnet and one is glass. Can you find the ruby? Can you separate the garnet from the glass with your polariscope?

Yes, the ruby would be the only one which would give a DR reaction in the polariscope test. No, (as with the dichroscope both the garnet and the glass would give SR reactions.

You are looking at two faceted, colorless stones that show visible dispersion and great brilliance. One is a diamond and one is a zircon. Can you separate them with your polariscope?

Yes, the diamond would test SR and the zircon would test DR.

Two translucent white stones look very similar, one is a milky type of chalcedony, and the other is a white moonstone. Can a polariscope test be used to separate them? If so, what would each gem's reaction be?

Yes, chalcedony (as an aggregate) gives an AGG reaction (always light) to the polariscope test, while moonstone (being a crystalline gem of the monoclinic system) tests DR (blinks light and dark when turned).

You have a colorless gem which you are told is phenakite (RI = 1.66). You have water, Refractol, and methylene iodide. You immerse the gem in each and get these results: in water: very high relief, in Refractol: moderate relief, in methylene iodide: the piece disappears. Can you estimate the RI of this gem? Is it consistent with phenakite? Do these results prove it to be phenakite? Are there different possible results which would disprove it being phenakite?

Since the gem shows no relief (disappears) in methylene iodide whose RI is 1.74, the gem has a lower RI value than that. Since it does show relief in Refractol whose RI is 1.56 you know that it has an RI higher than that. So its RI lies between 1.56 and 1.74. Since phenakite's RI is 1.66, the gem could be phenakite. These results do not prove it is phenakite, however, as there are other colorless gems with RI's between 1.56 and 1.74, like Danburite, for one. Other results that could have disproven an identity of phenakite would have been: if the gem disappeared in Refractol (its RI would be below 1.56) or if it showed relief in methylene iodide (its RI would be above 1.74). Such results would be incompatible with phenakite.

You have a group of colorless faceted gems, including: rock crystal quartz, white zircon, phenakite, white sapphire, diamond and white topaz. You'd like to find the diamond. They are not the same size or shape. You also have a gem reference book and a refractometer (and have been trained in how to use it). Which gems can be eliminated by learning their RI readings? Which ones cannot be eliminated that way? Using any test from this, or any earlier lesson, tell me how you'd find the diamond.

All the listed gems (except diamond and zircon) have RI's below 1.80 and so could be ruled out as being diamond which has an "OTL" reading on the refractometer. So you'd be left with the diamond and the zircon. There are many correct ways to answer how can these two be separated but two of the ways would be 1) Specific Gravity (zircon is much heavier than diamond), since they aren't the same size and shape you couldn't do it by hefting or comparing measurements, but you could do it by hydrostatic weighing and 2) Optic Character (diamond is SR, zircon DR) you could do a polariscope test or check with a loupe for doubled facets to find the zircon.

You have been given a gem to examine microscopically. Which type of lighting would be best suited to determine each of the following: The likelihood that it is synthetic or enhanced with dye? The fine points of its cut and polish, and the degree of wear and tear it has sustained? Its clarity?

a: Diffused brightfield lighting is best for this, as it can reveal color zoning and growth patterns that might indicate synthetic origin, or unusual concentrations of color that might indicate dyeing or diffusion. b: Overhead (or reflected) light would enable you to see nuances of polish and the exact number and placement of facets. Any scratches, nicks or chips on the surface would also show up clearly. c: Darkfield illumination is best for clarity observation as it displays any inner structures at the highest possible relief.

Why would bubbles have particularly high relief, and why would they generally be distinguishable from rounded crystals by using polarized light?

Bubbles are filled with gases which are less dense and therefore of much lower refractive index than gems, their relief, therefore, would be high. Most crystals (with the exception of those in the cubic system) will flash dark and light when polarized light is shone through them and a polarizing lens is turned above the image. The gases inside bubbles would not do that.

Why did I stipulate "certified as natural" by a laboratory in the above?

A flawless gem, by definition, has no inclusions or other microscopically visible internal characteristics that might help an ordinary gemologist or jewler identify it as of natural origin and/or unenhanced status. The specialized equipment of large laboratories, like those of GIA, would therefore be necessary. In rare cases, there are no current tests which can absolutely rule out certain enhancements, and the best such labs can guarantee if this is true is "no signs of enhancement or synthetic origin were determined".

Cat'seye and star stones are generally used in rings and bracelets, rather than in brooches, tie pins, earrings or pendants. Why do you think this is so?

1) Cat'seye and star stones are oriented in such a way that their phenomena are well displayed on the center of the dome of the cabochon when light is hitting it perpendicular to the base of the cabochon. This is what happens when you hold your hand out to see a ring or bracelet (or when they are viewed in a jewelry display case), but gems that hang or are worn vertically do not show their phenomena to good advantage, as the light is mostly hitting the gem obliquely or parallel to the base.

In Hall in the discussion of tumbling, the statement: "gem fragments of similar hardness may be turned..." Why does the author specify that they must be of similar hardness?

If the gems being tumbled together are not all of approximately the same hardness, the softer ones will not only be worn down by the abrasive grit in the barrel, but also by contact with the harder stones in the mix. In my own first tumbling effort many years ago, when I did not know this, I opened the barrel after a couple of weeks, to find some of the gems (the harder ones) just barely worn, and some of the softer ones almost gone.

The vast majority of hololith gem creations (especially the interlocking ones) have historically been made from jade, with a smaller number constructed from jaspers or chalcedonies. Why do you think these materials are favored?

Aggregate materials like jasper, agate, chalcedony and especially the jades: nephrite and jadeite, are very tough, which means that they will not easily break when the forces of the carvers' tools are used to make and/or separate relatively thin areas. This is particularly true for interlinked forms which require a lot of force on a small "thread"of material attaching one piece to another. Single crystal materials, being less tough, break much more easily.

Why would it take longer to get a good polish on a concave facet than on a flat one?

In order for a gem to have a good polish the surface must be made absolutely uniform, and smooth to a microscopic degree. Polishing a curved surface to this level, is much more difficult and time consuming than doing the same with a flat one. Picture as in woodworking, for example, trying to sand a flat table top, versus sanding a curving table leg and trying to get each of them perfectly, and uniformly, smooth.

Your friend wants an untreated gemstone and has found a dealer with some beautiful golden beryls. The dealer assures him that they have not been heated. He asks for your advice. What do you tell him?

You might make sure that your friend understands the difference between "unheated" and "unenhanced." Most likely he is under the impression that they mean the same thing. Few people who have not studied gems realize the vast number of treatment possibilities there are. You could also mention that a lot of the golden beryl in the market has been irradiated. A possible suggestion would be that he ask the dealer, point blank, whether the gem has had any enhancement at all. (On the other hand you might like to just keep your mouth shut, and smile, and agree that they are lovely).

You walk into a jewelry store with your brand new gift ruby ring, and the emerald brooch you inherited from Aunt Minnie. You want the ring sized, and a new closure soldered onto the brooch. You ask the jeweler for the estimated charges including dismounting and remounting the gems. She says dismounting will not be necessary. What should you do?

The safest thing to do would be to walk right out and find another jeweler. The new ruby ring could be glass filled, the emeralds are almost certainly oiled in either case the heat from the jeweler's torch (even when methods are used to keep the gems isolated from the heat) can do major damage. Even if the gems were completely unenhanced, there is still the possibility of damage from inclusions due to thermal expansion.

Think back to what you learned in Lesson 7 about faceting: Will a 20 mm wide split boule yield a 20 mm round brilliant?

A cylindrical boule that is split down the center will have a depth of 10 mm, so theoretically the maximize sized round stone you could get would be 10 mm. In practice it would have to be even less than that in order to insure there was no window.

Why should larger diameter boules make for less obviously curved striae?

Think of cutting a cherry in half and compare the rate of curvature of the outer edge with an orange cut in half. The larger the circumference the more gradual is the curve. When you are looking at a faceted gem you are looking at a tiny little sector of a boule the larger the boule it was cut from, the less curvature you will see.

If you were an honest seller of synthetic ruby jewelry why might you pick flame fusion material, and if you in the same business dishonestly, why might your choice be pulled synthetics instead?

An honest synthetic ruby seller will go for the lower priced flame fusion material whereas the dishonest one might opt for the more expensive, but harder to identify, pulled material.

What is the purpose of rolling the string in the dry table sugar, wouldn't the string itself provide a surface for crystallization?

The tiny sugar crystals not only provide a surface, they also provide a pattern to follow so that as the sugar in solution crystallizes, the ones that are already present get larger. Without this pattern to follow the sugar crystallizes in a more disorganized manner that is not so attractive.

Why would a YAG and strontium titanate doublet be a better diamond simulant than either material by itself?

A doublet made with YAG on top and strontium titanate on the bottom would be relatively hard (YAG is 8.5) and have less dispersion than strontium titanate alone (which has too much) and more dispersion than YAG (which has too little).

Dealers who supply facetors with gem rough may sometimes tumble it first. Why?

Gem rough that comes from primary sources or eluvial sources may have internal fractures, partial cleavages, or ungainly shapes. Tumbling the rough simulates what happens as weathered-out gems travel down streambeds, breaking off weak areas and wearing away protrusions. The tumbled rough is more desirable to the facetor as it is cleaner, and better shaped for good recovery; so they will pay more for it.

What type of terrain do you think is most likely to yield eluvial deposits? alluvial ones?

Flat terrain, especially that which is in an area that is arid, is most likely to yield eluvial gems. It is not surprising, then, that we find eluvial peridot at a place named "Peridot Mesa" (mesa = table top). Alluvial gems however, are most likely to be found in the foot hills and valleys of mountain ranges. (Where did the '49ers look for gold nuggets?).