Blue lace agate is an agate variety with pale blue and white, lace-patterned banding. Until 2017, its primary source was a single, now-defunct mine in Namibia, although similar material has been found elsewhere. Blue lace agate is a vein agate; in Namibia, it formed in dolerite of Jurassic age. It is used in lapidary as a semiprecious gemstone.
The primary source of blue lace agate for several decades was the privately-owned Ysterputs Mine (also spelled Ysterputz)[4] on Ysterputs Farm 254 in Karasburg West, ǁKaras Region, Namibia.[3][5] The mine was owned by the late George Swanson[4] and was in operation from 1962 until January 2017; as of December2023[update] its future is uncertain.[6] Most of the mineralogical data on blue lace agate originates from recent analysis of material from Ysterputs.[4][6]
The geological formations at Ysterputs are not unique to this one location; it is possible that there are other occurrences of blue lace agate in Namibia or neighboring South Africa that remain unexploited.[4] Other localities have also produced a blue lace agate very similar to that found at Ysterputs, including the Lapurr Range in Turkana County, Kenya.[3] Blue lace agate or other blue-colored chalcedony has also been found in Georgia,[7] Malawi, Zambia, Turkey, and at other small mines in Namibia.[8]
Blue lace agate has an overall color of pale or light blue.[3][9] It has a distinctive, wavy,[5] lace-like pattern that consists primarily of blue, spherulitic chalcedony bands layered with bands of white, micro-granularquartz.[6] Unlike most agates,[1][6] the majority of the chalcedony in blue lace agate is the length-slow variety, quartzine; this suggests that it formed in fluids with a high salinity. Also present are bands and tiny clusters of angular, rhombohedral quartz crystals with thin chalcedony overgrowths, some of which are visible to the naked eye and have well-formed faces.[6]
Blue lace agate often contains a central area of massive (unbanded) chalcedony or a central vug.[4] The vugs are often lined with clear or blue druzy quartz crystals.[6] Crystals of calcite, gypsum, siderite, or ankerite may also occur in the vugs or on the outer surfaces of the agate.[4][6]
Rare cubic crystals of blue chalcedony up to 9 millimetres (0.35in) in size have also been found in vugs and on plates at a single location in the Ysterputs Mine.[4][6][10] While previously thought to be pseudomorphs after fluorite, they are likely pseudomorphs after melanophlogite.[6]
The color of blue lace agate is believed to be due to Rayleigh scattering of light by tiny cavities, inclusions, or sub-microscopic particles of amorphoussilica within the agate.[4] In some specimens from Ysterputs, a fraction of the chalcedony bands appear fluorescent green under short-wave ultraviolet light due to trace amounts of uranyl ions.[6]
Geology
At Ysterputs, blue lace agate formed as hydrothermal vein deposits in the Tandjiesberg sill, an igneous intrusion of dolerite dating to the Jurassic period (roughly 183 million years ago).[6] The sill intruded the Whitehill Formation shale of the Ecca Group, part of the Karoo Series of marine sedimentary rocks dating to the Permian period.[6] The dolerite sill caused low-grade regional metamorphism of the surrounding shale and partial melting at its base. This created a hydrothermal system that carried a silica-rich, saline solution and volatiles from the underlying Karoo rocks into fractures in the sill resulting from a shear zone.[4][6] The silica precipitated out of the solution in successive bands under varying conditions, forming the agate veins.[6] The veins are typically 20–30 millimetres (0.79–1.18in) thick or up to 60 millimetres (2.4in) thick where the agate spans the whole width of the main fissure.[4][6]
The color and thickness of the agate banding tends to be symmetrical on both sides of the fissure walls around a central plane.[4][6] A layer of coarse, yellow-green dolomite,[6] previously thought to be calcite,[4] was deposited on the fissure walls prior to the agate and may still be attached in some specimens. Coating cavities in the veins is a smectite clay originating from weathered dolerite that has been previously identified as nontronite, although this could not be confirmed analytically.[4][6]
Blue lace agate has been widely marketed as a lapidary material for jewelry and other aesthetic purposes. Particularly interesting specimens, such as those with crystal coatings or cubic chalcedony, are also sought after by mineral collectors.[4][6]
References
1 2 "Agate". mindat.org. Hudson Institute of Mineralogy. Retrieved 11 October 2025.
↑ Pabian, Roger; Jackson, Brian; Tandy, Peter; Cromartie, John (2016). Agates: Treasures of the Earth. Firefly Books. pp.134–135. ISBN978-1-77085-644-8.
↑ Wicht, Jo; Miller, Duncan (28 September 2021). "Blue chalcedony pseudomorphs from Ysterputs, southern Namibia". Yacimientos Minerales en FMF. 3 (126): 3–12. Retrieved 13 November 2025.Originally published in the October 2021 edition of Mineral Chatter, the newsletter of the Cape Town Gem & Mineral Club.
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