Amethyst in sandstone
Virtual Museum ID: 19-NCM03
The color in amethyst from most localities is unevenly distributed in the individual crystals. In amethyst geodes, it is often most intense in the growth zones under the rhombohedral faces (at the tips). Occasionally the color is deeper under either the r or z rhombohedral faces, giving the crystal a pinwheel appearance when viewed from the top. In prismatic crystals, the color may appear in phantom-like thin layers, while in scepters and skeleton quartz the color is often concentrated along the edges, and accompanied by smoky zones. Despite the intense color, the content of iron occupying Si positions in amethyst is rather low, in the 10-100 ppm range (Dennen and Puckett, 1972).
When heated to more than about 300-400°C, amethyst loses its violet color and often turns yellow, orange or brown, and then resembles the quartz variety citrine, but depending on the locality and the temperature during the heat treatment it may also turn colorless or - rarely - green (Rose and Lietz, 1954; Neumann and Schmetzer, 1984).
The information listed below relates to the current holding location or collection that the sample is from, and whether the item is viewable at that location or is part of a private collection. Coordinates are given as guides, and we remind you that collecting specimens from these locations is not allowed. Caution is advised visiting such sites and Below BC assumes no responsibility for any injuries or trespassing charges that may occur as a result of the viewer entering these sites.
Original Collection:Chamber of Mines of Eastern BC (NCM)
Virtual Museum ID:19-NCM03
Date Added to VM:2019-06-11
Sample Origin:Passmore, BC
Specific Site:Valhalla Complex
Datum:11 (NAD 83)
Primary Features:Amethyst in sandstone
Primary Mineral Formula:SiO₂
Advanced Geological Information
The following section provides geological data relating to the specimen or the site it was collected from, when available. Information has been obtained from various sources including private and government datasets but may not be up to date. Any geological time periods or ages listed often relate to the primary geology of the area, and may not be the actual date of an event such as mineral formation.
Geological Formation:Valhalla Complex
Geological Period:Middle Jurassic/Late Cretaceous
Stratigraphic Age:174.1 - 66.0 Million Years
The Main iolite occurrence is located 2 kilometres north of the Blu Starr occurrence (MINFILE 082FNW259), adjacent to Highway 6 on the Blu Starr gemstone property. The Blu Starr property is situated at the confluence of the Slocan and Little Slocan rivers near Passmore, approximately 25 kilometres west of Nelson. The deposit consists of four zones: the main I1 zone to north, the I2 zone to the south and the smaller I3 and I4 zones.
The Slocan Blu Starr property lies within the southern portion of the Valhalla-Passmore Gneiss Complex, in the Passmore Dome. The Valhalla Complex consists of a high-grade metamorphic core with outwardly dipping metamorphic layering and foliation. Heterogeneous sequences of biotitic schist (pelitic schist), quartzo-feldspathic gneiss (psammitic gneiss), amphibolite gneiss and minor marble, calc-silicate gneiss, quartzite, metaconglomerate and ultramafic rocks make up the Valhalla assemblage of metamorphic rocks.
Coarse iolite crystals are completely embedded in the hostrock and occur within brownish quartz veins, along the contacts between the veins and the host anthophyllite and in biotite zones. The crystals grade from transparent, blue-violet or grey iolite at the core, to pale green translucent to opaque aphanitic alteration rims. Iolite occurs as both single crystals—some exceeding 10 centimetres in diameter—and as crystalline masses, some up to several kilograms in size. Iolite from the Blu Starr property is trichroic, appearing blue-violet, honey yellow and pale blue-grey. At the I1 zone, gem-quality amethyst crystals occur in late-stage pegmatite dikes and miarolitic pockets associated with clear quartz crystals and schorl tourmaline. Approximately 1 kilogram of amethyst crystal pieces suitable for cabbing and faceting was extracted from the I1 zone.
The iolite-anthophyllite layer has a characteristic rough, hummocky appearance with a brown to dark green weathered surface. The iolite is composed of gedritic anthophyllite, quartz, garnet, biotite, plagioclase feldspar with minor clinoamphiboles and iolite and trace corundum. The layer is coarse-grained (0.5 to 2 centimetres) and is characterized by interlocking blades of gedritic anthophyllite and irregularly distributed heavily included garnet porphyroblasts up to 20 centimetres in diameter. The I1 zone, the largest known accumulation of iolite on the Blu Starr property, is exposed for more than 25 metres along strike and has an average thickness of 4 metres. The smaller I2 zone has an average thickness of 2 metres.
The Blu Starr sapphire deposit was discovered in 1991, followed by the discovery of the Blu Moon sapphire deposit (MINFILE 082FNW263) to the northwest in 1993. From 1991 to 1995, approximately 10 tonnes of sapphire-bearing rock was hand mined, yielding approximately 10 kilograms (50 000 carats) of coarse rough sapphire from Blu Starr and 1 kilogram (5000 carats) from Blu Moon (Press Release, Anglo Swiss Resources Inc., December 18, 2012). The property was acquired by Anglo Swiss Resources Inc. in 1995. That same year, Marylou Coyle, PhD, was contracted to study the deposits and make recommendations for development. In 1996, the first organized geological studies of sapphire deposits were conducted, leading to the discovery of aquamarine beryl crystals in quartz-tourmaline pegmatitic dikes. In 1997, a 150-tonne composite bulk sample was extracted from the Blu Moon deposit and sent for processing. Smaller hand samples were taken from Blu Starr and other gem showings on the property. In 1998, a small gem garnet deposit was discovered on a mountainside near the Blu Starr deposit and a 2-tonne bulk sample was extracted. That same year, an extensive mineralized zone of crystalline graphite was discovered in the Tedesco area and the Sapphire Hill occurrences were found near the Blu Moon deposit. Three zones of iolite mineralization, including the I1 (or Main Iolite), were also found north of the Blu Starr deposit in the fall of 1998. One tonne of sapphire-mineralized rock was extracted from Sapphire Hill and two 1-tonne bulk samples containing approximately 25 kilograms of coarse rough crystal and gem iolite were extracted from the I1 and I2 iolite zones. In 1999, a detailed geological examination of the iolite zones was completed.
In 2000, Hampton Court Resources partnered with Anglo Swiss Resources in a joint venture. Exploration by Hampton Court focused on evaluating the potential of placer claims along the Slocan River, west of the Blu Starr deposit. The potential of alluvial deposits along the Slocan Valley was assessed with respect to potentially commercial deposits of gemstones, including garnet, iolite and sapphire. Work that year consisted of 8.5 kilometres of ground-penetrating radar, surface geological mapping and preparation of a report titled Mineralogic Evaluation of the Slocan River Placer Claims. At the same time, exploration continued on other areas of the property. Thirteen new sapphire occurrences were identified, as were occurrences of amethyst quartz, rose quartz and titanite. Ten new iolite-anthophyllite occurrences were discovered along the Rainbow Horizon, and the New Star claim was staked to cover the northern extension of the iolite-anthophyllite–bearing Rainbow Horizon. A potentially large and economic gem garnet occurrence was identified in the Tedesco area. Bulk samples were extracted from the Tedesco garnet deposit (2.76 tonnes) and the I1 Iolite deposit (greater than 100 tonnes). More than 1000 carats of red garnet gem rough were recovered from Tedesco and more than 5 tonnes of specimen crystal and coarse rough gem material were recovered from the I1 Iolite (Assessment Report 26537).
In 2003, the joint venture with Hampton Court lapsed. Work on the property was suspended until 2008, when a graphite exploration program was undertaken. Ground geophysics was used to explore for graphite up to 200 metres in depth. Three diamond drillholes totalling 812.9 metres were completed. In 2010, 525.9 kilometres of airborne geophysical surveys were completed across the entire property. A limited ground survey of soil sampling and prospecting was carried out on the region of known graphite occurrences. In 2012, an induced polarization survey was carried out over the Tedesco graphite showing.
Two 1-tonne samples of mineralized rock were extracted in 1998, yielding over 25 kilograms (1000 carats) of high-grade iolite crystal ore (Press Release, Anglo Swiss Resources, December 9, 1998; January 15, 1999).