Jeffrey Mine grossular is one of the great Canadian garnets: transparent to translucent crystals in cinnamon, sherry-orange, honey, pink, colorless, and green, commonly bright enough to look gem-cut before they ever left the matrix. The classic look is hessonite—orange grossular, Ca3Al2(SiO4)3—perched as lustrous, complex dodecahedral crystals on dark syenitic or pale albitite/rodingite matrix, often with contrasting green diopside. The best examples have a limpid, “barley sugar” glow, sharp geometric faces, and the fine growth striations that make Jeffrey crystals instantly recognizable to experienced collectors.
Photo: Wikimedia Commons
The mineralogical setting is as important as the beauty. Jeffrey was a huge chrysotile asbestos operation in the ultramafic belt of southern Québec, and the collector minerals formed where granitic and syenitic rocks, albitites, and rodingites interacted with serpentinized dunite and peridotite. Calcium- and aluminium-rich fluids produced the spectacular calcium-silicate assemblages for which the mine became famous: grossular, vesuvianite, diopside, prehnite, pectolite, wollastonite-group material, and rare species such as spertiniite and jeffreyite.
Photo: Wikimedia Commons
Collectors prize Jeffrey Mine garnet because it combines three traits that seldom occur together: cabinet-specimen aesthetics, gem transparency, and a well-documented classic locality. The most coveted pieces show orange hessonite crystals standing cleanly on contrasting green diopside or pale matrix; rarer still are deep pink grossulars, colorless or pale pink crystals with green cores, and large transparent individuals from the late-1990s discoveries. The mine’s long inactivity and flooding transformed what was once obtainable material into a finite classic. Today, fine pieces are bought as much for locality pedigree as for crystallography.
Search for specimens: View all garnet specimens from Jeffrey Mine, Quebec, Canada
Jeffrey Mine lies at Val-des-Sources in Estrie, Québec, the town long known to collectors and old labels as Asbestos. Modern locality strings should use Jeffrey Mine, Val-des-Sources, Les Sources RCM, Estrie, Québec, Canada; older labels may read Asbestos, Shipton Township, Richmond County, “Johns-Manville Mine,” or “Jeffrey Quarry.” The town voted in October 2020 to replace the name Asbestos with Val-des-Sources, so historic labels are not necessarily wrong, but they need interpreting.
The mine was an open-cast chrysotile asbestos deposit roughly 2 km across and about 350 m deep. It exploited a cylindrical orebody in serpentinized ultramafic rocks, with the valuable asbestos fibers chiefly in serpentinized peridotite rather than dunite. The same ultramafic setting that made Jeffrey a major asbestos mine also made it an extraordinary mineral-specimen locality: red syenite, albitite, granitic dikes, and rodingites in and around the dunite-peridotite body supplied the fractures and reaction zones where grossular crystallized.
The grossular is not a random dump mineral here. The great specimens came from specific fracture systems and rodingitic zones, especially where Ca-Al-rich alteration affected rocks in contact with serpentinized ultramafics. Many of the classic orange grossulars were collected when active mine benches intersected a productive rodingite vein; because benches cut the vein only intermittently, production of fine garnet specimens came in pulses rather than as a steady output.
Mining began in the late nineteenth century. By the mid- and late twentieth century Jeffrey was not only a major asbestos producer but a legendary collecting name, internationally known for orange grossular, multicolored vesuvianite, prehnite, pectolite, and rare species. Attempts were made to continue or revive production by underground methods after open-pit difficulties increased, but specimen access declined sharply as mining slowed, the pit became unstable, and pumping stopped. The best collecting areas for grossular were reported underwater by mid-2003, and later collecting opportunities became exceptional rather than routine.
Public collecting inside the mine was not generally allowed. For years, special guests, university groups, scientists, workers, and organized club excursions were the main routes by which specimens emerged. The mine management also maintained a public “mineral site” near the installations for about 25 years, stocked with potentially interesting material brought out from the mine rather than dumped. That site made Jeffrey minerals accessible to countless visitors, but it has not been a source of fresh mine-run material for a long time. Modern would-be field collectors should treat the mine as a closed industrial site with asbestos, unstable pit walls, flooding, and property restrictions; old-stock specimens are the safe and legitimate way most collectors encounter Jeffrey garnet today.
The collector garnet from Jeffrey Mine is principally grossular, most famously hessonite, the cinnamon-orange to sherry-orange variety of grossular. Mindat also records chrome-bearing grossular and andradite from the locality, and older mineral lists include additional garnet-group names; however, when collectors say “Jeffrey Mine garnet” without qualification, they usually mean grossular, and most market specimens are sold as grossular or grossular var. hessonite.
Color is the locality’s first calling card. Orange hessonite ranges from honey and peach through deep cinnamon to intense reddish orange. Pink grossular is much rarer and has a distinct collector following, especially the 1998 material. Green grossular occurs as chrome-bearing material and as green-cored crystals; colorless and pale pink examples are known and may be gemmy enough for faceting. Brownish-orange and sherry tones are also characteristic.
Crystal form is another strength. Jeffrey grossular occurs as well-formed dodecahedral and trapezohedral crystals, including rhombic dodecahedra, trapezohedra, and combinations with complex growth features. Some crystals show striking striations and surface patterns related to growth sectors and optical anomalies studied in the mineralogical literature. Fine pieces may have glassy faces, beveled edges, and visible internal growth structures without losing transparency.
Typical collectible crystals range from a few millimeters to around 1–2 cm. Notable crystals in the literature and specimen records reach larger sizes: classic hessonite crystals were reported up to about 3 cm in early gemological work, individual Jeffrey grossular crystals up to about 4 cm are known, and a documented transparent crystal from a late-1990s specimen measured 4.2 cm across. Such sizes are exceptional, especially when the crystal is sharp, undamaged, and well positioned on matrix.
The most desirable matrix pieces combine orange grossular with green diopside, giving the sharpest color contrast. Other associated minerals include prehnite, albitite matrix, syenitic matrix, pectolite, apophyllite on rare pieces, and wollastonite-group fibrous material around some pink grossulars. The pink 1998 material is especially distinctive because many crystals were found as floaters or on green diopside or white albitite matrix, whereas Jeffrey grossular is more commonly seen on darker syenitic matrix.
Quality is judged by transparency, luster, color saturation, crystal isolation, and freedom from bruising. The very best Jeffrey hessonites have a glowing internal orange, clean and reflective faces, and a balanced arrangement on contrasting matrix. For advanced collectors, unusual color varieties—deep pink, colorless, chrome-green, and pale crystals with green cores—can outrank ordinary orange pieces even when the crystals are smaller.
Jeffrey Mine grossular is a classic closed-locality material, so provenance matters. Old labels reading Asbestos, Jeffrey Mine, Johns-Manville, or Shipton Township can be valuable evidence rather than a defect, but vague “Canada hessonite” labels should be treated cautiously. Modern labels that use Val-des-Sources are geographically current; older labels using Asbestos are historically normal.
I would be most cautious about three issues: locality accuracy, condition, and undisclosed repair. The color and form of Jeffrey hessonite are distinctive but not unique in the world; orange grossular also occurs at other localities, and loose crystals can lose their diagnostic context. Matrix, associated green diopside, old collection labels, and reputable dealer history all strengthen a Jeffrey attribution.
Published and commercial descriptions of Jeffrey material focus on natural damage, contact marks, edge bruising, and specimen preparation rather than any routine color treatment. Garnet is not commonly “improved” in the way some gem species are, but specimen repair and stabilization are normal concerns for any valuable crystal-on-matrix piece. Check for glued crystals, filled chips, suspiciously perfect crystal-to-matrix junctions, and repaired matrix breaks, especially on high-value cabinet specimens with large exposed crystals.
Common condition issues include incomplete edge crystals, small contacts around the periphery, bruising on high points, internal fractures that can be mistaken for surface damage, and fragile matrix around diopside-rich specimens. Some Jeffrey crystals are naturally internally veiled or growth-zoned; this can add character, but it should not be confused with a repaired break.
Market availability is uneven. Small orange hessonite crystals and miniatures still appear regularly from old collections and dealer stock. Fine miniatures and cabinet pieces with gemmy crystals, rich color, and good matrix are much less common and can command strong prices. Deep pink grossular, large transparent crystals, and colorless or pale crystals with green cores are specialized rarities. The best examples are now largely locked in private collections, museums, or long-held dealer inventories.
At the end of 1996 and during the first months of 1997, the active workings crossed one of the mine’s classic orange-grossular veins. At Jeffrey this mattered enormously: the benches intersected the productive vein only at intervals of several years, so a single crossing could define what collectors saw on the market for a decade. This time the pocket was really a series of fractures, and it produced only a small number of top pieces—five good cabinet specimens and two miniatures, plus lesser material. A miner working a power shovel recovered the material, and in August 1997 he sold the whole lot to Jonathan Levinger of Montréal. The best small cabinet specimen was 6.6 cm wide, and the best miniature 3.5 cm; both were crystallized all around, carrying gemmy rhombic-dodecahedral grossular crystals up to 2.5 cm on green diopside. The rest went to the 1997 Denver show, where the best pieces entered major private collections.
The great pink-grossular day came on July 5, 1998, during a collecting outing organized by the Club de Minéralogie d’Asbestos. A few club members found what were described as the best pink grossulars ever collected at Jeffrey. They were not ordinary matrix hessonites: the crystals were lustrous, transparent, deep pink, and up to 1.5 cm, some as floaters and some on green diopside or white albitite. The white albitite was notable because Jeffrey grossular more often sat on dark syenitic matrix. A former Jeffrey miner found the most memorable pocket in a large rock and sold many of the pieces immediately to Marco Amabili. The crystals had been protected inside soft white fibrous masses of a wollastonite-group mineral, which helped them survive blasting and collecting. Fewer than 15 very high-quality specimens came from that discovery, and no later find of comparable pink grossular was reported from the mine.
The summer of 1999 produced one of Jeffrey’s strangest small marvels: white, colorless, or pale pink grossular crystals with bright green cores. In the best pieces, the green appeared as a spot in the middle of each crystal face, an orderly emerald pattern glowing through otherwise pale crystal. Most crystals averaged only about 4 mm, though one 9 mm crystal was noted in Marco Amabili’s collection. Some specimens carried cream-colored globular prehnite. The effect was so unusual that earlier thumbnails of similar bicolored grossular had been described at the 1998 Denver show as “dreamy,” because the green could be seen through the pinkish-orange exterior.
Also in May 1999, a collector cracked open a large dump rock and revealed a cavity measuring 17 x 40 x 50 cm lined with green diopside. Some diopside terminations carried orange grossular crystals. The best specimen from that rock measured 7.5 x 15 cm and displayed 14 orange garnets up to 1.4 cm individually. Jeffrey’s dump material could still surprise even after the mine’s great years: the right boulder could contain a miniature pocket history of the classic rodingite assemblage.
By June 2003, the bottom of the pit was already flooded to about 300 feet. When mining stopped, pumping stopped with it, and by July 2003 the pit was flooded to nearly 100 m. The best grossular collecting areas were underwater. The last organized collecting excursions were shadowed by slumping ground and shrinking safe zones; the directors of the local mineral club decided to stop mine collecting because the risk had become too high. That is part of why Jeffrey grossular feels different in the hand today. It is not merely a pretty orange garnet. It is a specimen from a vanished industrial landscape, from pockets now inaccessible beneath water and unstable walls.
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