Diopside from the Jeffrey Mine is one of the quiet signatures of a locality better known, at first glance, for world-class grossular and vesuvianite. The best pieces are not simply “diopside specimens” in isolation; they are Jeffrey specimens in the fullest sense—pale to apple-green sprays, bladed aggregates, tabular crystals, or glassy needles acting as the architectural stage on which orange hessonite, chrome-bearing grossular, prehnite, pectolite, and vesuvianite appear.
Photo: Wikimedia Commons
The mine’s mineralogical character comes from the contact between serpentinized ultramafic rocks and altered felsic dikes, especially rodingites. In that calcium-rich, hydrothermally altered environment, Jeffrey diopside developed with grossular-dominant assemblages that are instantly recognizable: green diopside beneath gemmy cinnamon-orange garnet, pale green diopside supporting pink grossular, acicular white diopside with prehnite, or unusually transparent tabular diopside with vesuvianite in the late-stage collecting zones.
Collectors prize Jeffrey diopside for association, texture, and locality context more than for single-crystal size. It is a locality where a mat of diopside needles can make a garnet specimen sing, where pale green diopside seen through transparent grossular gives the illusion of green inclusions, and where rare tabular, colorless crystals appear as a refined accent in a vesuvianite pocket. The material is also historically charged: Jeffrey was a giant chrysotile asbestos mine, a classic Canadian mineral locality, and a source of specimens that entered major private and museum collections during the 1970s, 1980s, and the important late discoveries of the 1990s and early 2000s.
Search for specimens: View all diopside specimens from Jeffrey Mine, Canada
The Jeffrey Mine lies at Val-des-Sources, formerly Asbestos, in Les Sources RCM, Estrie, Québec. It was an open-pit chrysotile asbestos mine developed in serpentinized ultramafic rocks of the Asbestos ophiolite. The classic collector minerals occur not in ordinary asbestos ore, but in altered dikes, albitites, syenitic bodies, and rodingites enclosed in or cutting the serpentinized dunite and peridotite.
The asbestos orebody was described as a large cylindrical body, roughly 600 by 900 meters in horizontal section, dipping about 65 degrees southwest. The pit itself reached enormous scale: about 2 kilometers across and roughly 350 meters deep in the early 2000s descriptions. From south to north, the mine area exposed pyroxenite, serpentinized dunite, and serpentinized peridotite, with economically useful chrysotile fiber chiefly in the serpentinized peridotite. The diopside-bearing collector assemblages are tied to the same alteration system that produced grossular, vesuvianite, prehnite, pectolite, wollastonite, and other calcium silicates.
Mining began in the late nineteenth century and the Jeffrey name became inseparable from the town’s identity. The locality became famous to collectors during the second half of the twentieth century, especially for orange hessonite grossulars on dark matrix, chrome-green grossulars, multicolored vesuvianites, sharply crystallized prehnite, pectolite, and diopside-rich combinations. During the 1970s and 1980s, Jeffrey specimens were comparatively available; by the late 1990s, reduced asbestos production made significant new discoveries increasingly sporadic.
Public collecting in the pit itself was never simply open access. The mine was an industrial property, and entry depended on permission, escorts, club excursions, or work inside the mine. The Club de Minéralogie d’Asbestos obtained permission in the 1990s to run seasonal collecting excursions, usually within defined safe zones. After ground instability and flooding became serious, collecting opportunities narrowed sharply. By the time the major open-pit operations ceased and pumping stopped, important lower collecting areas were submerged; the locality is now essentially a closed classic, with specimens circulating mainly from old collections, dealer inventories, and earlier mine finds.
The most important diopside-related finds are usually discussed through their associations. In late 1996 and early 1997, a rodingite vein yielded deep orange grossulars associated with acicular green diopside. On July 5, 1998, a Club de Minéralogie d’Asbestos collecting day produced exceptional pink grossulars on green diopside and white albitite. In May 1999, a large rock from the dumps was cracked open to reveal a cavity lined with green diopside crystals, some carrying orange grossulars on their terminations. Later finds included prehnite on acicular white diopside and, in vesuvianite zones, rare transparent colorless tabular diopside.
Jeffrey diopside is recorded in prismatic and bladed habits, with white, lavender, and green colors. In collector specimens, it is most often seen as pale green to apple-green aggregates, acicular sprays, fine bladed crystals, or microcrystalline to crystalline bases supporting more colorful associated species. Good crystals may be vitreous and transparent to translucent, but many are included, fibrous-looking, or satiny because of close parallel growth.
The classic grossular-diopside pieces show diopside as green needles or elongated crystals penetrating, supporting, or partly surrounded by garnet. Orange hessonite, pink grossular, and chrome-bearing green grossular can all occur with diopside. In the most visually effective specimens, the diopside is not merely matrix: it creates contrast, lift, and color temperature. Orange grossular against green diopside is the iconic pairing; pink grossular on green diopside is rarer and more delicate; chrome-bearing grossular on diopside can produce a bright green-on-green effect that rewards magnification.
Diopside crystals of significant size are uncommon in the grossular-bearing assemblages. Most visible crystals are millimetric to around a centimeter, commonly as needles, blades, or sprays. Some documented specimens show grossular crystals perched on diopside terminations, and a notable 1999 cavity was lined with green diopside, producing a 7.5 by 15 cm specimen with fourteen orange garnets up to 1.4 cm. In the vesuvianite zone, transparent colorless tabular diopside to more than 1 cm was reported as a rare association.
Associated minerals are a defining feature of Jeffrey diopside. The most important are grossular, including hessonite and chrome-bearing varieties; vesuvianite, including manganese-bearing and chrome-bearing varieties; prehnite; pectolite; clinochlore; wollastonite; heazlewoodite; chromite; albite; and rodingite matrix. Less common or more specialized associations include apophyllite, manganite, groutite, native copper, and spertiniite in adjacent assemblages.
Quality in Jeffrey diopside is judged by four linked factors. First is association: diopside with gemmy grossular, sharp prehnite, or strong vesuvianite is far more desirable than anonymous massive material. Second is crystal definition: collectors prefer separated sprays, aerial crystals, or tabular individuals rather than dull, matted growth. Third is color and contrast: fresh pale to vivid green diopside beneath orange, pink, or green garnet is the classic look. Fourth is provenance: labels from old Québec collections, named miners, early dealer stocks, or documented late discoveries add real importance, because the locality is no longer producing in any normal collecting sense.
Jeffrey diopside is not known as a treatment-driven material. The main authenticity question is locality and association, not artificial enhancement. Because pale green diopside with grossular can resemble material from other rodingite or skarn localities, strong provenance matters: old labels, collector history, and matrix style are important. Jeffrey combinations tend to show the locality’s distinctive calcium-silicate assemblage—grossular on green diopside, prehnite or pectolite in association, chromite or serpentinized ultramafic context, and the color palette of orange, pink, white, and green.
Condition is a more frequent issue than fakery. Diopside sprays and blades can be brittle, edge-worn, or bruised; garnets perched on diopside may show contact marks from blasting, trimming, or pocket extraction. Some matrix is friable enough that old specimens may be stabilized, repaired, or mounted. Acrylic bases are common on thumbnails and miniatures, and a base by itself is not a warning sign, but glue on the specimen should be checked under magnification. Look carefully for broken diopside needles, crushed tips, and garnets detached and reattached to green matrix.
The asbestos context deserves practical respect. Not every attractive Jeffrey diopside specimen is hazardous in normal display, but the locality is an asbestos mine, and specimens may retain serpentine, chrysotile-bearing matrix, or dusty fracture surfaces. Avoid sawing, grinding, sanding, air-blasting, aggressive brushing, or ultrasonic cleaning of suspect matrix. Keep friable pieces in a box or case, wash hands after handling dusty material, and do not store loose, shedding serpentinite debris with ordinary collection material.
Rarity varies sharply by style. Small green diopside aggregates and diopside-bearing grossular miniatures appear with some regularity on the secondary market. Fine pieces with aerial, well-defined diopside crystals; pink grossular on green diopside; significant orange hessonite perched on diopside; or transparent tabular diopside with vesuvianite are much scarcer. The market is now largely old-stock and collection-dispersal driven. Jeffrey labels remain highly marketable, and the best grossular-diopside combinations compete with classic Canadian garnets rather than with ordinary diopside specimens.
The late 1996 to early 1997 pocket has the feel of a last bright flare from the old Jeffrey. Active workings cut a rodingite vein that had produced classic garnets before, but by then the reduced scale of asbestos mining meant fewer chances and fewer specimens. One pocket—really a series of fractures—produced deep orange, nearly red grossulars on acicular green diopside. Only five good cabinet specimens and two miniatures came out, plus lower-grade material. The pieces were collected not by a visiting collector with a hand tool, but by a miner operating a power shovel. In August 1997, the miner sold the whole lot to Jonathan Levinger, the Montréal collector-dealer. The best pieces were small in number but large in consequence: crystallized all around, with gemmy rhombic-dodecahedral grossular crystals to 2.5 cm on green diopside.
The July 5, 1998 collecting day is one of the great modern Jeffrey stories. The Club de Minéralogie d’Asbestos had organized one of its mine excursions, and club members found the best pink grossulars ever collected at the mine. The surprise was not only the color, but the matrix. Jeffrey grossular is most familiar on dark syenite, yet these lustrous transparent pink garnets occurred as floaters or on green diopside and white albitite. Marco Amabili and Francesco Spertini collected good pink grossular on green diopside while digging in the albitite, but the day’s memorable pocket was found in a large rock by a former Jeffrey miner. The crystals reached 1.5 cm, unusually large for that pink style, and the best specimens were few: fewer than fifteen reached very high quality.
A third episode belongs to the mine dumps in May 1999. A collector cracked open a large rock and found a cavity measuring 17 by 40 by 50 cm lined with green diopside crystals. Some of the diopside crystals carried orange grossulars on their terminations—the kind of association that explains why Jeffrey diopside is so often discussed as the structural partner of the garnet. The best specimen from that find measured 7.5 by 15 cm and displayed fourteen orange garnets up to 1.4 cm. For a locality where diopside commonly forms supporting sprays rather than large show crystals, that cavity remains one of the clearest examples of diopside as the visual foundation of a major Jeffrey specimen.
A field report from a Jeffrey collecting trip gives the ground-level version of what collectors actually searched for. Visitors first had to be members of the Asbestos mineral club, then hope for a place on one of the organized trips. At the mine they received safety instructions and were told what had recently been exposed by blasting. They went by bus to the blast area and searched the granite and contact zones: cognac hessonite in the granitic areas, and grossular of various colors—clear to green—near the contact between serpentinite and hard white rock. In the white blocks, veins and pockets filled with green diopside could contain pink garnet. One collector described a specimen with more than twenty clear pink garnets sitting on green diopside crystals; the largest garnet was about 1 cm, on a 5 by 3.5 cm matrix. Another had pink garnets of similar habit, and a third showed a 1.5 cm garnet on matrix with minor diopside. The verdict was simple and unforced: it was “a very good day.”
The vesuvianite discoveries of 2002 and 2003 added a different diopside note. The collecting zone was restricted to a safer upper east part of the pit after instability made most of the mine unsuitable for club excursions. The old 2440 level area, important in 1978 and 1988, had yielded purple, pink, yellow, and green vesuvianite from a rodingite dike in serpentinized dunite. Ground movement re-exposed part of the dike in 2002. In that zone, pockets only centimeters apart could produce different forms and colors of vesuvianite: emerald to dioptase-green crystals, yellowish green crystals with purple cores, “purple-cap” crystals with deep purple terminations, forest-green pointed crystals, and deep amethyst-colored clusters. Diopside appeared there rarely as transparent, colorless tabular crystals over 1 cm, a refined and easily overlooked association in a zone dominated by spectacular vesuvianite.
Amethyst
Quartz
Fluorite
Tourmaline
Malachite
Azurite
Rhodochrosite
