Green Grossular Garnets
The mixing of Garnets in infinite combinations makes the naming of Garnets species and varieties difficult. In the marketplace, it is a free-for-all when it comes to trade names. Gem dealers want to appeal to buyers by using familiar and colorful names like "Cranberry" Rhodolite (purple-red Rhodolite), "Champagne" Garnet (yellow-brown Andradite), and "Mandarin" Garnet (dark orange Spessartine or dark orange Hessonite).
Gem dealers also commonly apply their own trade names based on the location of gem deposits, such as Mozambique Garnet (determined by our investigation to be Standard Pyrope), Tanga Garnet from Tanzania (determined to be Malaya), Umbalite from Tanzania (determined to be Malaya), Maralambo Garnet from Madagascar (determined to be Malaya) and JTV's Massasi Bordeaux Garnet from Tanzania (determined to be Malaya). Confusion arises when dealers fail to provide the appropriate variety names or even species names for these Garnets. JTV in particular takes liberties with nomenclature, trademarking many new names for Garnets such as Mpito Color Change Garnet from Kenya, Vermehlo Garnet (Pyrope-Amlmandine) from Mozambique, and Serengeti Spessartite Garnet from Tanzania, all touted as new and rare discoveries. Such trade names are generally not used by gemologists, but a few trade names such as Tsavorite, Rhodolite, Malaya and Mali Garnet have become widely accepted as variety names.
Graph of All Gem Garnets
The graph below shows results for over 500 Garnet gems tested by this researcher as part of an ongoing study conducted since 2010. This is the first time a diagram of the composition of all gem Garnet varieties, as determined by magnetic susceptibility and refractive index, has been published. A broad sampling of color is represented, as well as many rare and unusual Garnets. Species and variety names are color-coded to match the color of their graph points. For the sake of clarity, the numerous Grossular color variety names are listed on the left side of the graph rather than at their graph points. You can zoom your page view to 125% or more to see details. Due to overlapping graph points, not all 500 points on the graph are visible.
The Hoover method primarily measures iron and manganese in Garnets. Low concentrations of metals such as chromium and vanadium, which have low magnetic susceptibilities, contribue little or nothing to magnetic measurements. Grossular Garnet is an example. The low magnetic susceptibility we can measure in green Grossular Garnets (under 2 SI) may have little if anything to do with the coloring agents chromium and vanadium. The magnetism we detect could be due to entirely to iron (Fe3+) from the Andradite end-member.
Because the positioning of Garnet graph points on a Hoover diagram is mainly determined by iron and manganese content, it is not possible to accurately predict variations in Garnet color and color intensity by the location of those graph points. Color variations may be due to small variations in chromium/vanadium content, and in some cases possibly to color processes such as intervalence charge transfer. Two Garnets of entirely different color can have the same major composition and share the same graph point location, as illustrated by the 2 gems below.
Color Change Garnets
Graph of All Gem Garnets (over 500 Samples)
As purely descriptive terms, hybrid names convey useful information about the extent of a Garnet's hybridization. But when detailed information about any individual Garnet's composition can readily be determined by using the RIMS method, we don't need to create new species names in order to classify Garnets. We can simply use the standard mineralogical classification system, which classifies an individual specimen by its primary end-member component (i.e. the species with the highest percentage composition). Our RIMS graph method determines the primary species by the trisection in which a gem's graph point falls. A Malaya Garnet known to contain 40% Pyrope, 35% Almandine and 25% Spessartine is simply classified as a Malaya variety of the Pyrope species.
Readers can click on Gem Garnet Classification to view a proposed Garnet classification system developed during this study. For Garnet species and varieties that overlap in composition and color, there are no clear boundaries, but we can attempt to make meaningful separations (see page 6 for more details).
Color Change Pyrope
Color Change Spessartine
When we do the calculation for the Malaya Garnet graph point shown above, we find that this particular gem is 58% Pyrope, 22% Spessartine and 20% Almandine. Readers can do this simple calculation after measuring the above lines on their computer screen with a ruler. We can also use mathematics software that can be set up to perform such calculations automatically.
A photograph of the Malaya Garnet represented by the above graph point is shown below, along with a representation of its major composition. Percentages of possible other minor components such as Grossuar or Uvarovite have not been calculated and are not shown in this representation.
Percentages of the 3 major components of a Malaya Garnet
This researcher considers Malaya to be primarily a variety of Pyrope that has unusual color: red, pinkish red, pink, brown, brownish pink, orange, brownish orange, orangey red and even near-colorless. Gems are often lighter in tone than Standard Pyrope gems, and these lighter Malayas often exhibit color-shift when viewed under incandescent light.
Three Lines Intersect the Malaya Garnet Graph Point
Orangey Red Malaya
Without any calculations, the approximate composition of the Malaya Garnet is instantly known simply by looking at the position of its graph point in relation to the 3 end member species of the ternary. Positioned toward the Pyrope end member, and equidistant from both the Pyrope-Almandine and Pyrope-Spessartine boundary lines, we know this gem is predominantly Pyrope with smaller amounts of Almandine and Spessartine in roughly equal amounts. The magnetism of this Malaya Garnet is derived equally from the presence of 2 metals: iron (Fe2+) and manganese (Mn2+).
Malaya Garnet Graph Point
Percentage of composition for each end member species is calculated by measuring the full length of a line, then the length of the segment furthest from the apex (between the graph point and where the line ends at the ternary boundary), and finally dividing the far segment length by the full line length. We do this 3 times, once for each line initiating from its end member apex. The 3 percentages of end members should add up to 100%.
Graph of Malaya Garnets (RI range 1.735- 1.779, SI range 12.17- 30.89)
The olive-brown Garnet from Kenya and the purple Garnet from Bekily, Madagascar pictured above are both Color Change Pyropes, or if you prefer, Color Change Pyrope-Spessartines. Both gems change to pink color in incandescent light. They have identical refractive indexes and magnetic susceptibilities. Both have the identical major composition of 51% Pyrope and 49% Spessartine. But a slightly higher concentration of chromium/vanadium (which is magnetically undetectable) is responsible for purple color in the oval gem. The shared graph point of these 2 gems is shown below, along with a spectrometer graph showing higher chromium/vanadium content in the purple Garnet.
Color Change Garnets with Identical Primary Composition
Garnets of Different Color Can Have the Same Primary Composition
As examples of mixing in small percentages, Green Grossulars such as Tsavorite and Merelani contain only about 5% Andradite (iron, Fe3+). Ions of chromium (Cr3+) and vanadium (V3+), which impart the green color found in these Grossulars, are derived from even slighter mixing with Uvarovite (Cr3+), Knorringite (Cr3+) and Goldmanite (V3+) Garnet species. That is to say, chromium and vanadium ions partially replace aluminum in the B site of the chemical formula for Grossular gems. The chromium/vanadium oxides that give green Grossulars all of their color make up less than 2% of the gem's weight, and can be as low as 0.1% or less.
Light Pink Malaya
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Some varieties shown on the All Gem Garnet graph above have refractive index ranges that do not match exactly the ranges published by GIA. For example, the low RI for Rhodolite Garnet in this study is 1.738, while the low limit given by GIA is 1.740. The high RI for Standard Pyrope found in this study is 1.77, while the GIA high is limited to 1.756. GIA classifies Pyropes with RI's higher than 1.756 as Pyrope-Spessartines.
The graph above clearly shows that Pyralspite Garnet species mix with each other much more freely than do Ugrandite Garnet species. Ugrandites are composed primarily of one end member or another, with not much in the way of intermediate examples. With the exception of Uvarovite, all Ugrandites tested are in solid solution between Grossular and Andradite, with graph points falling along the Grossular-Andradite boundary line. We have not found any Grossular-Andradites with true intermediate composition, meaning no graph points fall further than a third of the away from the closest end member along the Grossular-Andradite boundary. Gemologists often refer to Mali Garnet as a Grossuar-Andradite variety, but Mali is better characterized simply as a Grossular Garnet.
Malaya is a Variety of Pyrope
Malaya Garnets can also be light pink in color. Some pink Malayas may also have a slight amount of purple color (see the pear pictured below), and show weak color shift by flashing to red in incandescent light. Light pinks also show color change from pink in daylight to yellow in fluorescent light due to manganese. These are Pyrope-Spessartines, and the pink daylight color is due primarily to chromium.
Masasi Bordeaux Garnet™ (# 1)
Pyrope and Grossular are allochromatic Garnet species, while Almandine, Spessartine, Andradite and Uvarovite are idiochromatic. The strong colors and magnetic responses seen in Pyrope and Grossular are due to mixing with the idiochromatic species. In reality, every Garnet gem (except perhaps some red Spessartine gems) is a mixture of idiochromatic and allochromatic components. The amount of mixing can sometimes be very small.
When we examine Garnets with a spectrometer, we see that chromium/vanadium is important to color in all varieties of Pyrope Garnet, with small amounts resulting in red, pink, purple, blue and green colors. Manganese (Mn2+) primarily controls orange and yellow colors in Pyralspite Garnets. Andradite Garnet colors such as brown, red and yellow are likely due to Fe2+-Ti4+ and/or Fe2+-Fe3+ charge transfer processes, while green color is the result of iron (Fe3+) and chromium/vanadium. Green color in Grossulars is primarily the result of chromium/vanadium, while orange and pink colors are caused by manganese (Mn2+ and Mn3+). Iron (Fe3+) is often colorless (cryptic) in Grossulars. More research is needed to provide a more complete picture of color in Garnets.
Based on the location of graph points in this study, we consider Standard Pyrope, Rhodolite, Chrome Pyrope, Pastel Pyrope and Malaya to be varieties of the Pyrope species. Color Change Garnet can be classified as either a variety of Pyrope or Spessartine, depending on a particular gem's composition. This researcher does not consider Color Change Garnet to be a sub-variety of Malaya, as do some gemologists. Study results show that Malaya is a variety of Pyrope in the vast majority of cases, but we do find a small percentage of Malayas that are primarily Spessartine. There is considerable overlap in composition among different Pyralspite varieties, particularly between Rhodolite, Malaya and Standard Pyrope. Distinguishing between these can at times be subjective (see page 6).
Determining Percentages of 3 End Member Species
More often than not, graph points of gems fall inside the boundaries of a ternary rather than along the boundary lines that connect two end members. This is particularly true of Rhodolite (purple graph points) and Malaya (yellow graph points) shown in the All Gem Garnet graph above. Positioning toward the center of the ternary indicates that all 3 end-members of the ternary are major components of the gem. Shown below is a graph point for a Malaya Garnet located near the center of the Pyrope trisection of the Pyralspite ternary. This indicates that Pyrope, Almandine and Spessartine are all major components of the Malaya Garnet.
The exact percentages of each end member species can be easily calculated. We simply use a straight edge to draw a straight line that starts at an end member apex, passes through the graph point, and ends at the opposite boundary. We do this 3 times, one line from each of the 3 end member apexes.
The Tanzanian Garnet trademarked in 2011 by Jewelry Television as Masasi Bordeaux Garnet™ (photo below left, point #1 shown in the graph above) would be classified by this researcher as a light-colored brownish orangey pink Malaya (trade name "Imperial" Malaya). These Garnets are colored by manganese and chromium/vanadium. Magnetic testing (RIMS analysis) of Masasi gem #1 (below left) purchased from JTV reveals a composition of Pyrope and Spessartine in roughly equal proportions: 50% Pyrope, 49% Spessartine, and 1% Almandine. Some Grossular is also likely present.
Magnetism in Gemstones
An Effective Tool and Method for Gem Identification
Bright Orange Malaya
Pale Orange Malaya
Three Orange Malayas with Spessartine as the Primary Component
Near-Colorless Orange Malaya .22ct
Malayas are generally classified by GIA as belonging to the Pyrope-Spessartine species, but our study shows that the majority contain significant amounts of all 3 end-members (Pyrope, Almandine and Spessartine), while fewer are either Pyrope-Almandines or Pyrope-Spessartines. Other researchers who have performed chemical analyses on Malaya Garnets using an electron microprobe report that a small amount of Grossular (under 5%) is also commonly present.
On average, we found that Malayas have greater Spessartine content than do Standard Pyropes. However, only 5 samples out of 106 Malayas tested in our study were found to have Spessartine as the primary component. Two of these Malaya Spessartines were barely over the Pyrope-Spessartine boundary. Below is the composition graph for 87 Malaya Garnets tested. Point #2 represents the Malaya with the highest Spessartine content.
Near-colorless Malayas are very rare. We have encountered only one example (pictured below), and such Malayas have not been described anywhere outside this website. The near-colorless gem has a slight orange tint due to manganese. The small size and depth of the gem also contributes to a lighter appearance. This Malaya Pyrope contains the least amount of Spessartine of any orange Malaya tested (62% Pyrope, 36% Spessartine, 2% Almandine). It has the same major composition as pale pink Malaya, but the concentration of chromium is too low to induce pink as the predominant color. However, there is sufficient chromium to induce pink fluorescence under long wave UV light.
Malayas with orange color due to Spessartine content are far less common in the marketplace than reddish stones. Orange Malayas can be orangey red, pure orange, brownish orange, pale orange, and near-colorless with just a hint of orange. Some orangey red Malayas will shift color to brownish orange when viewed under fluorescent light. As already mentioned, most orange Malayas are primarily Pyrope, but a few have been found to be primarily Spessartine.
The 3 strongly colored orange gems pictured below are all from Tanzania. These contain a higher percentage of Spessartine relative to most other Malayas, but each still has Pyrope as the primary component. The dark reddish orange Malaya on the left contains nearly as much Spessartine as it does Pyrope (42% Pyrope, 39% Spessartine, 19% Almandine).
Two other Masasi gems tested were also Pyrope-Spessartines containing 1) 58% Pyrope, 41% Spessartine and 2) 62% Pyrope, 35% Spessartine respectively. Each also contained a small percentage of Almandine.
These compositions are similar to that of pale "Imperial" Malayas and pale pink Malayas. These Garnets are not unique to JTV. We found Malayas of similar color and composition to Masasi Bordeaux Garnet™ originating not only in Africa, but also in Sri Lanka and Madagascar.
“Imperial” is a trade name or marketing term that is most often applied today to Malaya Garnets that have a brown-orange-pink color (reminiscent of "Imperial" Topaz) and an intermediate tone that is neither overly dark nor overly pale. Generally, the plot points for Imperial Malayas are centrally located on the Pyralspite ternary, indicating a mixture of Pyrope, Almandine and Spessartine, with Pyrope as the primary component. The composition of "Imperial" Malayas can be loosely differentiated from red Malayas, which tend to fall near the Pyrope-Almandine line (high Almandine), from pale pink Malayas, which tend to fall near the Pyrope-Spessartine line (high Spessartine), and from orange Malayas, which tend to fall to the right of the Malaya range due to higher Spessartine content.
"Umbalite" Garnet (pictured below left) is a red Malaya Garnet from Umba Valley, Tanzania. Umbalite is a trade name rather than a distinct variety of Garnet. These Garnets often have a hint of orange color mixed with the red. Brown color is unusual in Malaya Garnets. The Brown Malaya shown below right is from Kenya.
Masasi Bordeaux Garnet™
Causes of Color
We know that a Garnet's color cannot always be attributed to the chromophores present in its primary end member. The orange of Spessartine (Mn2+) and red of Almandine (Fe2+) can be attributed to their primary species content, but the red of Pyrope Garnet is not due to Pyrope content (Mg2+ magnesium). The red is derived from Almandine (Fe2+ iron) and Uvarovite/Knorringite/Goldmanite (Cr3+/V3+ chromium/vanadium). Very small percentages of chromophores from other Garnet end members can dramatically affect color. As another example, the color of blue Color Change Garnet is not derived from it's primary component Pyrope (Mg2+ magnesium), but rather from Spessartine (Mn2+ manganese) in combination with minor Goldmanite (V3+ vanadium) and Uvarovite (Cr3+ chromium) content (Schmetzer et. al. 2009).
Light Pink Malaya (Daylight and UV Fluorescence)
We encountered one light orange Malaya Garnet (pictured below) that has a yellowish tint not found in other Malayas. This gem is primarily Spessartine in composition (52% Spessartine, 30% Pyrope, 18% Almandine), with body color similar to “fanta” Spessartines, but with more yellow. This Malaya was incorrectly sold as a standard Spessartine, which would have significantly greater magnetic susceptibility. We refer to this gem as a Malaya Spessartine, in contrast to the 3 orange Malaya Pyropes pictured above.
Surprisingly, this yellowish orange Malaya Spessartine (below) fluoresces red under long wave UV light due to chromium. As we would expec, it also shows a Pick-up response to a magnetic wand, due mostly to manganese content. Manganese does not quench fluoescence from chromium, but no other high-manganese orange Malayas that we have tested show fluorescence.
The likely reasons that yellow color (from manganese) and red fluorescence (from chromium) can coexist in this orange Malaya are: 1) the concentration of chromium is so low that it is not visible as red body color but is detectable under long wave UV light, and 2) the concentration of iron is low enough that it imparts little or no red body color, and is too low to quench all the fluorescence from chromium. Fluorescence in idiochromatic gems of any kind, including standard Spessartine and Malaya Spessartine, is rare.
Light Yellowish Orange Malaya Spessartine
Daylight Color and LWUV Fluorescence
Though almost colorless, the small Malaya above has relatively high magnetic susceptibility (SI 17.62), containing enough manganese to be easily picked up by an N-52 magnet. This is an indication that most of the manganese in this Garnet is cryptic (cannot be detected visibly as color but can be detected by magnetic response). Although it has never been reported, we suspect that completely colorless Pyrope-Spessartines can exist if the concentration of manganese (Mn2+) is low and chromium/vanadium concentration is also very low or absent.
Some light pink Malayas from Tanzania fluoresce pink or red under long wave ultraviolet light due to chromium, as does the oval Malaya pictured below. This contradicts other gemological resources, which describe Malaya Garnet, whether primarily Pyrope or primarily Spessartine in compsoition, as inert to UV light.
Even among gemologists, there is no consensus on how Garnets should be named or classified. At times gemologists simply ignore disparate composition in favor of common color, or common color phenomena such as color change, when naming Garnets. For example, purple Almandines are sometimes referred to as Rhodolites, even though their composition is very different from that of the reddish purple Pyropes (Rhodolites) of similar color that were originally named in the nineteenth century. We feel that using color or color phenomena as the primary parameter for classifying Garnets is a mistake that creates confusion. Gems of different species can appear identical, and color change can occur across species.
Some gemologists (Manson/Stockton, Hanneman) have created new species names that represent hybrids such as Pyrope-Almandine and Pyrope-Spessartine, which refer to intermediate Garnets composed of two major species. These would have graph points located along the mid-section of a boundary line between two end members. GIA now regards these two hybrids as distinct species in addition to the 6 primary species.
51% Pyrope, 49% Almandine
34% Pyrope, 66% Spessartine