Precious or semi-precious?
It’s a question every rock hounder or geologist has asked at the beginning of their journey.
In this article, you’ll learn all you need to know about what makes them different.
Precious vs Semi Precious Stones (Explained)
As it happens, the monikers precious and semi-precious are nothing more than marketing terms created years ago by jewelers and sellers of “precious gems” to add a heightened sense of value to certain gemstones used in their adornments, making them sound more valuable than they actually are.
Precious and Semi-Precious stones prepared for use in the making of jewelry are more commonly referred to as gemstones and are typically cut and refined minerals.
There are exceptions, however.
These gemstones are better known as precise rocks or organic resources.
Here are a couple of examples that fall under this category; amber and jet.
As with most things, beauty is in the eye of the beholder and the value that gemstones have to some may be greater than to others as their favorites.
Value, however, is driven by rarity, purity and the cut of the stones.
Ironically though, while diamonds are considered the most precious, they are not the rarest.
These stones maintain their status as precious due to their unrivalled popularity and brilliance.
Semi-precious stones are considered relatively abundant in nature and thus, coupled with their softer Mohs ratings and lower luster, are not as valued.
In a second note of irony, Tanzanites are rarer than diamonds but, due to their softness, are less valuable.
Purity is an interesting one.
This typically has more to do with classification by gemologists regarding the number of inclusions present in a gemstone when it is being evaluated.
Gemologists will also often use practical industry language to classify each gemstone. For example, diamonds are made of carbon (C).
While they come in few colours, precious gemstones are able to retain their hue and luster much better over time with daily wear.
Semi-precious gemstones, on the other hand, offer a wide range of hues but tend to appear duller with regular wear and some of them are quite sensitive to chemicals, changes in temperature or even sweat.
Many gemstones are crystalline formations and because of this they can be further categorised by varieties, groups, species, dispersion, specific gravity, luster, hardness, cleavage, fracture, and refractive index.
Another way that gems are graded is by their hardness via the Mohs scale.
Precious gems usually rate higher on this scale, with diamonds being the highest at 10. Rubies & Sapphires follow at 9 and Emeralds come in between 7.5 and 8.
Semi-precious gems tend to have lower ratings, starting at around 7.5 and descending from there.
This makes them susceptible to scuffing, scratches, and other wear and tear that makes them lose their luster over time.
Overall, there is no real actual difference between the two types of stones, but the accepted list of precious stones is this:
List of Precious Stones
These gemstones are coveted for their brilliance, rarity, uniqueness and lasting luster.
These stones have a very high value in comparison to all other gemstones.
List of Semi Precious Stones
Here a list of semi precious stones:
- Black Onyx
- Blue Topaz
But, all other gemstones outside of the precious list fit the bill, so to speak.
While lower in value, the variety of colors and the wider availability of these stones makes them highly sought after for jewelry and other adornments.
In comparison, even the highest quality semi-precious stones are much more affordable than the lowest quality precious stones.
How do you spot precious or semi-precious gemstones in the wild?
Gemstones in nature look more like rocks and almost nothing like the cut and polished versions most people are used to seeing in stores, museums and pictures.
If you are interested in hunting for natural gemstones, start with purchasing a copy of an illustrated book on gemstones.
It would also be good to visit any local rock & mineral museums in your area or look up pictures of the various rough gemstones you are interested in on the internet.
In most cases, the rock and mineral museums in the town/city will display types of stones that can be found in the area somewhere in their displays.
This would be an ideal place to start.
Identifying rough gemstones is a process of reviewing their mineral qualities, streak and luster.
Each has their own particular qualities that can be catalogued to help with identification.
Checking a rough gemstone’s streak is done by rubbing it across an unglazed material such as the back of a ceramic tile.
The color that the stone leaves on the surface is called a streak.
Usually, but not always, the color of the gemstone’s streak is the same as the color of the refined (cut) gemstone.
E.g: Hematite is black when polished, but it leaves a red streak when rubbed against an unglazed ceramic tile.
Rough gemstones, typically crystalline structures, sparkle and shine when refined.
Check gemstones for their mineral shape to start the identification process.
Minerals can be placed in five basic categories:
- General – minerals without a definitive shape.
- Botryoidal – minerals that appear similar to bunches of grapes.
- Reniform – minerals that resemble a kidney shape. E.g., Hematite.
- Tabular – minerals with a flat crystal shape.
- Acicular – minerals with thin, needle-like crystals.
Again, luster refers to how a stone’s surface reflects light. Rough gemstones typically appear dull or greasy. In some cases, they can appear glasslike, metallic or milky.
E.g. Brazilian Blue Sapphires look blue-gray and African Blue Sapphires have angled surfaces with a brilliant midnight blue crystalline look.
Identifying rough stones by color is not the best way to identify the gem hiding inside, but it can sometimes work.
E.g. Tiger’s Eye in rough form looks like small multicolored banded blocks.
Rough Hematite can appear like common 3/4-inch driveway gravel (gray or a dull black).
Rough Turquoise can look like a band of blue on an ordinary looking rock.
It goes without saying that the more experienced hounders will have a better mental catalogue of examples like this, but even they will typically stick to other forms of identification and only use color as a guessing game for themselves for fun to see if they are right at the end of the process.
Cleavage in rock-hounding refers to the way the stone breaks across a surface. Gemstones break in one of several ways:
- Flat flakes break into one piece.
- Rhombic breakage occurs on several planes at diagonal angles.
- Cubic chips refer to stones that break across three planes at right angles.
- Long blocks result in breakage in two planes.
Hopefully, this information helps in understanding the differences between precious and semi-precious gemstone classifications and the basics on how to find them in the wild when rock hounding.
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