Rhodolite Garnet: Gemstone Information
Rhodolite Garnet derives its name from the mountain rhododendron (Rhododendron catawbiense), a magenta-coloured bloom which grows in the mountains of North Carolina, where rhodolite was first discovered in 1882. The original colour is described as ‘pale rose-red inclining to purple like that of certain roses and rhododendrons’: a rich rhododendron purple colour without any brown tint. The colour sets the range of RIs for this variety. However, almandine-bearing pyrope garnets whose constants fell within the range but whose colour was adulterated by, in particular, brown tints and variable tonal qualities have been traded as rhodolite such that the name no longer defines the colour. As a consequence almandine-bearing pyrope garnets whose colour matched that of the adulterated rhodolites but whose RIs were out of the range of rhodolite (sensu stricto) were also traded as rhodolite. The outcome being that over time the RIs range for ‘rhodolite’ has increased. Additionally, adjectival
colour prefixes have been introduced such that the integrity of the name rhodolite is no longer robust. The most desirable colour for rhodolite is purplish red of a medium tone. Large gems tend to be darker and more cranberry red with beautiful violet flashes; however, larger stones +5 cts, with poor transparency tend to be over-dark and unattractive.
A light, almost purple-pink coloured fine ‘silk-free’ rhodolite occurs in the Tanga region (towards the Kenyan border), Tanzania. Some colour modifiers have been added to the term ‘rhodolite’: these trade names, apart from grape garnet, retain the financial advantage of rhodolite soubriquet.
This material is called ‘raspberry’ because its fine purplish pink colourresembles that of the fruit. Discovered in early 1987, it is a member of the pyrope-almandite series found in the Kangala area of Tanzania, and has
an RI of 1.76.
In 1998 in the Slocan Valley, located in south-eastern British Columbia, Canada, garnet-bearing feldspar-rich pegmatite sills and dikes were discovered that produced cranberry-red pyrope-almandine crystals, frequently
+10 cm in diameter, that are compositionally similar to rhodolite from Tanzania. Cranberry to pinkish red rhodolite found in Nigeria is mostly highquality cabochon grade as most stones tend to be very slightly to moderately included.
Cherry rhodolite is found in the Umba River Valley region of Tanzania and displays a bright cherry-red colour.
The name was introduced to address the problem associated with colour variation and need to retain a robust definition of rhodolite. By branding the colour, dealers were able to develop quality standards for a gem that
had the colour of grape juice but had previously been brigaded with rhodolite (sensu lato). One confusing aspect is that the original purplish red to violet garnet mined in the Orissa state of North-west India and known as grape garnet has been variously reported as an intermediary between both spessartine and almandine and pyrope and almandine. However, published chemical data states that these contain +50% pyrope molecule.
Similarly coloured garnet discovered later in Fazanda Balisto in Tocantins, Brazil (1997), has been described as pyrope-almandine. Garnet production has been described as 40–50% rhodolite-pyrope colour and about 50% grape colour. However, analysis of ‘burgundy’ coloured garnets from alluvial deposits in Tocantins indicated that the ‘burgundy’ garnets are members of the almandine-spessartine series and comprised mainly of almandine. Similarly almandine of a rich grape colour has been reported from Tanzania and Madagascar. The issue of colour varieties is further muddled by modifying colour descriptions such as rich cranberry. Material can be traded indiscriminately as facet-rhodolite garnet-grape, grape garnet (rhodolite garnet) or raspberry/ grape based solely on colour.