A Beginner’s Guide to Gemstones for Jewellers and Stone Lovers

Whether you’re a jewellery enthusiast, a collector, a budding gemmologist or simply someone who appreciates the beauty of these precious stones, learning about the different types of gemstones is a fascinating journey.

From timeless diamonds to rare and exotic stones like alexandrite, each gemstone has its unique set of characteristics and properties that make it special and in this guide, we will:

Look at the most popular and well-known types of gemstones, providing you with valuable insights into their origins, characteristics.

Let’s begin our journey into the fascinating world of gemstones!

What Is A Gemstone?

Let’s start with one of the most fundamental questions about gemstones, which is “what is a gemstone?”

A broad definition is a mineral that is highly prized for beauty, durability, and rarity.

The problem with this definition is that not all gems are minerals because a mineral, according the the Collins Dictionary, is an inorganic substance occurring naturally in the earth but when it comes to gemstones, we have organic gems such as Pearls which are made by molluscs and Amber which is fossilised tree sap.

But let’s take a closer at the three highly prized characteristics in the above definition:

• Beauty

Beauty is in the eye of the beholder but colour, transparency, lustre and optical effects are all part of a stones beauty.

• Durability

A gems durability is a combination of its hardness, toughness and stability, which are all important for both how the gem is cut and best used.

• Rarity

Rarity is relative but gemstones are rarer than other types of mineral or metals, for example Diamond is a lot rarer than Iron.

Gemstones are a beloved and treasured part of human history, valued for their beauty, rarity, and symbolic and spiritual significance. With countless types of gemstones, it can be overwhelming to understand the differences between them and what makes each one special. Each gemstone has unique characteristics, properties, and uses, from precious and semi-precious gems to organic and synthetic varieties. In this article, we will explore the fascinating world of gemstones and delve into the main types of gemstones, discussing their history, symbolism, and significance. Whether you are a collector, jewellery enthusiast, or simply curious about these beautiful and mysterious stones, this article will provide a comprehensive guide to the types of gemstones that exist today.

Significance of Gemstones:

Gemstones have been valued for their beauty and rarity throughout human history, and they have also held symbolic and spiritual significance in various cultures. Here are some of the main reasons why gemstones are significant:

• Aesthetics:Gemstones are prized for their beauty and the way they reflect light, making them popular for jewellery and decorative objects.
• Rarity and Value:Many gemstones are rare and difficult to find, which makes them valuable and sought-after.
• Symbolism:Gemstones have been associated with different meanings and symbols throughout history. For example, diamonds are often associated with love and commitment, while emeralds are associated with growth and prosperity.
• Healing Properties:Some people believe that gemstones have healing properties and can be used to promote physical, emotional, and spiritual well-being.
• Cultural Significance:Gemstones have played important roles in various cultures and religions. For example, in Hinduism, the Navaratna gemstones are associated with the nine planets and are believed to bring good luck and fortune.
• Historical Significance:Gemstones have been used throughout history to signify wealth, power, and social status. Many famous gemstones, such as the Hope Diamond and the Koh-i-Noor Diamond, have fascinating histories and have been owned by royalty and other prominent figures.

In summary, gemstones have significance for various reasons, including their beauty, rarity, symbolism, healing properties, cultural significance, and historical significance

Precious vs Semi-Precious Stones

As we are talking about gemstone types, let’s have a look at one of the most commonly used ways of describing gemstones, which is Precious vs Semi-Precious:

• Precious Gemstones– this is Diamond, Emerald, Ruby and Sapphire (often called the Big 4)
• Semi-Precious Gemstones– everything else

The problem with this is that it is an antiquated and to be honest, completely stupid way of describing gemstones that we shouldn’t be using because there is now way to define the two!

People have tried to justify this by using factors such as rarity or value but both can easily discredited, for example:

• There are manygemstones including colour-change Alexandrite, Black Opal and Paraiba Tourmaline that are all rarer than the ‘Big 4’
• Prices for the ‘Big 4’ can range from less than $50 a carat to 6 or 7 figures per carat but many of the rarer gemstones will often range from hundreds to thousands a carat

GEMSTONE PROPERTIES

2- Durability

A high degree of durability in precious gemstones is necessary as this is the only factor that allows the beauty of a gemstone to be long-lasting, also only a durable gemstone can take and retain a good polish. Hardness is a measure of durability based on mineral’s ability to resist scratching and abrasion. Reaumur was the first one who proposed a method to measure the hardness of a mineral in 1722. He investigated the hardness a substance as the results of pressing together the edges of two right-angled prisms made of the substances to be compared. Later in 1822, a more practical means of assessing hardness was proposed by a German geologist Friedrich Mohs. He used ten species of minerals as standards of increasing hardness. These minerals in order of increasing Mohs hardness are 1) Talc 2) Gypsum 3) Calcite 4) Fluorite 5) Apatite 6) Orthoclase 7) Quartz 8) Topaz 9) Corundum 10) Diamond.

This means that Gypsum can scratch Talc, Calcite can scratch Gypsum and so on. The number 7 on Mohs’s scale is an important one, as any gemstone must be at least as hard as this if it is to withstand the action of grit in the air or on clothes.

Crystals tend to break or split parallel to certain definite directions. This property is called cleavage of a crystal and it is one of the consequences of those regular arrangements of the atoms which distinguish crystals from amorphous solids.  Cleavage is described as perfect, distinct or indistinct. Cleavage and fracture (atomic structure) affect the strength of a gemstone and the ease with which it can be worked. Extra care must be taken when working with gemstones that have one or more directions of perfect cleavage. It is worth noting that where the break is not related to the atomic structure (fracture) the resulting surface will not be flat or smooth.

3- Scarcity

In addition of being beautiful and durable, for a gemstone to be classified as a precious gemstone, it should be scarce. However scarcity itself does not guarantee that a gemstone will be a precious gemstone. It is largely an issue of supply and demand; the more that the demand outstrips the supply, the scarcer a gemstone becomes.

GEMSTONES ON MOHS HARDNESS SCALE

Although there are many methods and systems used to gauge a material’s hardness, the most common of these is the Mohs Hardness Scale. Mohs Hardness Scale, a system founded by Friedrich Mohs in 1812, is a type of chart used to test and contrast the hardness of different minerals. The scale, which can best be described as ordinal rather than linear or logarithmic, provides a rough measure of a mineral’s hardness based on its smooth surface resistance to scratching and abrasion. In other words, it allows our custom jewelry designer in Seattle and Bellevue to rank the hardness of a mineral by its ability (or inability) to scratch another known mineral.

Mohs Hardness Scale Simplified

Mohs Hardness Scale is based on 10 minerals, each of which is assigned an arbitrary value from 1 to 10. These minerals, along with their assigned value are:

When interpreting Mohs Hardness Scale, it is common to assume that a diamond, for instance, the hardest mineral listed on the scale, is ten times harder than talc, which is the lowest. This is not true, but is a common mistake. So when interpreting the Mohs Hardness Scale, it’s important to keep in mind that the scale is merely ordinal rather than linear. For example, corundum, with a value of 9 on Mohs Scale of Hardness, is twice as hard as topaz, with a value of 8, while a diamond is nearly four times as hard as corundum.

Using Mohs Hardness Scale

While Mohs Hardness Scale outlines the hardness or scratch resistance of ten common minerals, its true usefulness is in measuring the hardness of countless of other minerals and materials, almost all of which fall somewhere in between talc (1) and diamond (10). Gold, one of the most common minerals used by jewelers, generally ranks between 2.5 and 2.9 on Mohs Hardness Scale.

This number can be consistently ascertained by the ability of a particular sample of gold to scratch or leave an abrasion on gypsum (2), while being vulnerable to scratches when coming into contact with calcite (3) and all harder materials. Below we will take another look at Mohs Hardness Scale, as well as some common materials and how they compare in terms of hardness.

It is important to remember that the Mohs Hardness Scale, while certainly the most common measuring tool, is just one of the ways to identify a material and gauge its hardness and scratch resistance. The rock type, as well as its color, cleavage, luster and crystalline form, must also be taken into account, in addition to the material’s ranking on the scale.

Mohs Hardness Scale for Gemstones

The hardest and softest gemstones are…

As you probably already know, diamonds are the hardest substance on Earth, meaning that diamonds can scratch the surface of any other matter when in contact! On the other hand, as readers of the Laine Jewellery blog may remember, we have mentioned that pearls and mother-of-pearl are softer organic gemstones and could sustain abrasions more easily.

Gemstones have different levels of hardness. The “Mohs Hardness Scale” is a commonly used method in mineralogy and gemology to identify relative hardness. Developed by German geologist and mineralogist Friedrich Mohs in 1812, the Mohs Hardness Scale is a qualitative ordinal scale that characterises a mineral’s hardness in relation to other minerals but does not illustrate the absolute hardness.

The Mohs Hardness Scale describes the hardness of common minerals on a scale of 1 to 10, the larger the number, the harder the mineral, i.e. 10 being the hardest and 1 being the softest. Naturally, the hardest gemstone would be diamonds, while next would be gemstones from the corundum family (e.g. sapphires and rubies), which are the hardest known natural substances after diamonds. At the other end of the spectrum, talc is the softest mineral and is assigned to number 1. If a mineral’s hardness falls between two numbers, it can be described with .5. Let’s have a look at the hardness of different gemstones!

It would be hard to gauge actually how hard a gemstone is simply based on the relative numbers on the Mohs Scale. Here are the Mohs hardness levels of various daily objects to give you a better picture:

Masonry drill bit (for drilling tiles and concrete) 8.5 – 9

Steel nail 6.5

Glass 5.5

Copper coin 3.5

Fingernail 2.5

The hardness of gemstones is a useful reference. On the one hand, it reflects the wearability of gemstones. The harder a gemstone, the more scratch-resistant it is; while softer gemstones, such as pearls, would require more care and attention.

On the other hand, harder gemstones would achieve a better outcome and sparkle after cutting. This is the reason why diamonds, sapphires and rubies tend to have a more intense sparkle. Then of course, a good cut is needed to have the best results.

The hardness of a material may vary slightly with composition and also with state of aggregation. The measurement of hardness is very tricky and often a mark that looks like a scratch is actually a trail of powder left by the supposedly harder material! It is really not critical whether the hardness of a mineral is 5 or 5.5. Frac­tional hardnesses are reported where the literature has indicated an intermediate value. A range in hardness is much more meaningful, and the values reported in this book represent all values encountered in the literature. In only one case (kyanite) does the hardness of a mineral vary very widely even within a single crystal. In most cases the hardness range reported is very small (one unit).

References:
1- Color Encyclopedia of Gemstones, Joel E. Arem, VNR publications, New York.

BIRTHSTONE CHART

WEDDING ANNIVERSARY GEMSTONES

The traditional designation for wedding anniversaries go back to many years ago. The standard list, which includes each year for the first fifteen and each five years thereafter, was intended as a guide to the products which were considered proper to present to the married pair as gifts. The anniversary gift for the first fifteen years are inexpensive, for example, the first was paper, the second cotton, the fifth wood. Starting with thirtieth more expensive items (gemstone) were assigned to the weeding anniversary gifts as follows:

It should be noted that in actual practice, it is the husband who traditionally gives the wife a ring, necklace, bracelet, brooch, or pair of earring containing the gemstone to celebrate the anniversary.

Reference:
Birthstones and the lore of gemstones, Willard Heaps, Angus & Robertson PTY LTD,1971.

GEMSTONE CLARITY

Clarity: Clarity is about how pure a substance is. For instance, to be able to classify a gemstone as “flawless,” it must approach absolute clarity at 10X magnification. Clarity is assessed by the quantity of visible inclusions, fractures, or other internal defects that affect the transparency of the gemstone.

Inclusions, are divided in four groups:

1) solid inclusions which maybe of the same material as the host or one completely foreign to it; 2) internal cavities containing gas or liquid or both, sometimes bubble in an inclusion diminishes in size on warming the stone and finally disappears;

3) Cracks and fissures filled with gas or liquid which are termed flags or feathers;

4) Growth phenomena which includes zonal structures and irregular distribution of colors.

The standard terms for high grades of clarity are eye-clean, meaning there are no inclusions visible to the naked eye, or clean, meaning there are no inclusions visible even under 10X magnification.

COLOR OF GEMSTONES

Color gives both distinctiveness and character to a gemstone. May gemstones appear colored because either part of the white light traveling through them is absorbed within the mineral structure or reflecting the light within the gemstone. This absorption of the light is generally due to the presence of particular chemical elements and damage or irregularities in the crystal structure.  Most of the gems are colored due to presence of chromium, iron, manganese, titanium, and copper. For instance, chromium gives the intense red of ruby and brilliant greens of emerald. Copper gives the blue and greens of turquoise and malachite.

In colorless and cut gemstones, one can occasionally observe a play of color, which comes about through dispersion. When light enters a gemstone the various wavelengths are differently refracted, red the least and violate the most, so that the color spectrum is spread out. Gem minerals vary greatly in their ability to disperse light therefore different colors with different qualities are observed in gemstones. Color dispersion is especially high in diamonds where it produces a beautiful play of color that is called fire. 

Play of color in opal gemstone happens due to interference phenomenon. Interference happens when light falls on very thin, transparent mineral layers, it is reflected from both the upper and lower surfaces. Since the reflected rays have traveled different distances the wave troughs and peaks of the various wavelengths either coincide or are out of step.

A color is enhanced if they coincide but little or no color is seen for out of step wavelengths. Gemstone color chart can be found here.

GEM STONE COLOR CHART

Below is the color-categorized chart for the selected gemstones. Gemstones are categorized in ten colors including, red, pink, blue, green, yellow/gold, violet/purple, orange, white, black and, Star and Cat’s Eye Gems.

GEMSTONE FORM

Hexagonal system

Three of the four axes have the same length and are located in one plane. These axes intersect each other at an angle of 120 degree. Typical crystal shapes are hexagonal prisms and pyramids, as well as twelve-sided pyramids and double pyramids.

Trigonal system

Axes and the angles are similar to the hexagonal system. The difference is one of symmetry. In the case of hexagonal system, the cross section of the prism base is six sided; in trigonal system it is three-sided. Typical crystal forms of the trigonal system are three-sided prisms and pyramids, rhombohedra, and scalenohedra.

Orthorhombic system

Three axes of different lengths are at right angles to each other. Typical crystal shapes are pinacoids, rhombic prisms, Pyramids, and Double pyramids.

Monoclinic system

The three axes are each of different length, two are at right angles to each other and the third one is inclined. Gemstones from monoclinic system form basic shapes of Basal pinacoids and prisms with inclined end faces.

Triclinic System

All three axes are of different lengths and inclined to each other. Typical crystal forms are paired faces.

Below is the selected gemstone categorized by crystal system.

INCLUSIONS IN GEMSTONES

The term inclusion refers to any imperfection in the appearance of the gemstone. This includes any foreign body enclosed within a gemstone (gas, liquid, and solid), cleavage cracks, and color zoning. Inclusions can weaken the gemstone’s durability or affect the color of the gemstone, in this case inclusions significantly reduce the value of the stone. However, the existence of inclusions is not always bad. For instance, inclusions can provide positive identification and be the proof of originality. In this case, they may increase the value of the gemstone. Furthermore, sometimes inclusions are quite beautiful and make the gemstone more attractive. For instance existence of thin, golden, needlelike crystals of the material rutile change the value of the ordinary quartz. Considering the fact that flawless color stones are very rare, one should be immediately suspicious of any flawless gemstone (especially with today’s technology on fabricating synthetic gemstone). Loupe which is a special type of magnifier that is used by jewellers, can be used to examine a gemstone for any inclusion. Followings are the list of inclusions that are frequently found in gemstone:

1. Bubbles: As the name implies this inclusions look like bubbles of different shapes and sizes. It should be noted that very round and nice bubbles are usually indication of synthetic or glass imitated gemstone.
2. Cleavage fault: This type is actually a crack in the stone rather than an inclusion. It is often observed in topaz, diamond, feldspar, and kunzite.
3. Color zoning is the uneven distribution of gemstone’s color. This inclusion usually occurs as whitish or colorless parallel plates. Color zoning is frequently observed in ruby, sapphire, amethyst, and citrine.
4. Dendritic: these are the inclusions that give moss-agate its treelike structure.
5. Feather: usually refers to an internal crack
6. Halo or Disk-like inclusions: As the name implies, these inclusions look like disk (referred as halos). These inclusions are actually small fractures that result from the growth of zirconcrystals inside the host stone. Disk like inclusions are onserved in sapphire and garnet.
7. Needlelike: These are very long and thin crystals that resemble needles or thin fibers. These inclusions are frequently observed in tourmaline, ruby, sapphire, and garnet.
8. Rain: This inclusion looks like dashed lines resembling falling rain.
9. Sheaves: this is the inclusion of the mineral cacoxenite in amethyst
10. Silk: Thin intersecting needlelike crystals that exhibit a sheen similar to that of silk fabric. This inclusion is frequently seen in ruby and sapphire.
11. Solid: This inclusion refers to the presence of a solid crystal or mineral in the host stone.
12. Twinning: This inclusion looks like parallel cracks (planes). It is frequently observed in rubiesand sapphires which shoes their genuineness.
13. Veils: small bubble like inclusions arranged in layer structures. These inclusions can be wispy, flat or curvaceous.

GEMSTONE SPECIFIC GRAVITY (DENSITY)

Density, or specific gravity, is a bulk property of a mate­rial that is independent of direction and is uniform within a mass of material under ideal circumstances. In actuality, the density of a mineral varies widely, even within a single crystal, due to the presence of impu­rities, cracks, and bubbles. Density is a useful parameter in gem identification, so the problems in its determina­tion should be well understood.

Specific gravity is the ratio expressing the weight of a given material compared to that of an equal volume of water at 4°C. Thus, a specific gravity of 3 means that, at 4°C, one cubic centimeter of the material in question weighs 3 times as much as one cubic centimeter of water.

The density of a compound is a function of several factors, including chemical composition and crystal struc­ture. For example, consider diamond and graphite, both of which are crystalline forms of the element carbon. Diamond has a density of 3.5 because the carbon atoms are tightly packed together in the structure; graphite, with a much more loose, open structure, has a density of only 2.2.

The density of minerals within a solid solution series may vary linearly with change in composition. The effect of chemical substitution is seen dramatically in the case of the orthorhombic carbonate minerals aragonite and cerussite. Aragonite is CaCO3 and has a specific gravity of 2.95; cerussite, with the same structure, is composed of PbCO3 and has a specific gravity of 6.55! This clearly shows the role of lead versus calcium in the structure.

Specific gravities are usually measured with heavy liquids. A liquid is prepared, such as a mixture of bromo­form and toluene, to have a specific density value. An unknown material dropped into the liquid may sink, float, or remain suspended in one place within the liquid. If the material sinks, it is denser than the liquid, and if it floats it is less dense. If it remains at one level it has the same density as the liquid. Very accurate measurements of specific gravity can be made by changing the density of a column of liquid through temperature variations and suspending density standards in the column.

An alternative method of measurement is the use of so-called torsion balances, such as the Hanneman bal­ance and the Berman balance used by mineralogists. These devices are designed to weigh a sample first in air and then suspended in a liquid, such as water or toluene. The weights in both media can be measured quite accu­rately and specific gravities can sometimes be reported to two decimal places.

  A major problem in all density measurements is the presence of impurities within the crystal being studied. These impurities hardly ever have the same specific gravity as the host material, and their presence results in measurements that are of limited use for identification purposes. Surface tension may also “float” a mineral grain in both heavy liquids and a torsion balance, resulting in an erroneously low specific gravity measurement. Accu­rate density measurement involves absolute cleanliness, great care in specimen preparation, accurate tempera­ture control, and replicate measurements.

GEMSTONE SPECIFIC GRAVITY TABLE

Gems with perfect cleavage must be set carefully and worn carefully, as a sharp blow to the stone along a cleavage direction may easily split the gem. Spodumene is well known for its difficulty in cutting. Even topaz offers occasional problems to the cutter who is not aware of the cleavage direction, because it is virtually impossi­ble to polish a gemstone surface that is parallel to a cleavage plane.

References:
1- Color Encyclopedia of Gemstones, Joel E. Arem, VNR publications, New York.

2.https://www.wikigempedia.com/gemstone