Phlogging a dead horse?

May 9, 2019
Jo Wicht

Many of you are aware of my obsession with Blue Lace Agate, both from a lapidary point of view and with stones from the mine, as well as my curiosity as to how the mineral was possibly formed. Any new information that I come across, be it a new specimen or comment, has to be investigated. Recently it was Marco Campos-Venuti’s new book (Banded Agates: a genetic approach (2018) which set me off on the trail again because it has a chapter on Lace Agates. Marco’s theory on their formation suggests two separate fluids were involved: firstly a saline brine solution, dependent on rainfall, and secondly a fluid from a greater depth associated with a low temperature hydrothermal system of probably less than 100 °C. Their interaction would be responsible for the formation of Lace Agates.

The words salt and brine made me think of the mineral halite, and query whether that was perhaps the mineral that was pseudomorphed by the chalcedony at Ysterputs, rather than fluorite. I bought a new specimen of Blue Lace at the beginning of last year and comparing that to a photograph of halite I found on the internet showed the appearance was so similar.

Blue Lace Agate specimen      



Being of more a creative and imaginative nature than a true scientist, I sent these two views to Duncan, who agreed that the likeness was amazingly similar and suggested he post a query on the Mindat Mineralogy Message Board asking whether halite might be a possibility for replacement by chalcedony, seeing as it dissolved far more easily than fluorite ( was duly done, and the single reply (from Alfredo Petrov) suggested it could possibly also be melanophlogite, and even if it wasn’t that, fluorite was the most likely mineral to have been replaced.

I had once heard of melanophlogite, having come across it when doing research for my website ( but its looks and descriptions didn’t quite fit with examples in my collection. Likewise the profiles of the points of my specimens didn’t quite fit that of examples of fluorite I had seen either.

Melanophlogite was written up in an article by Marek Chorazewicz on where he had found it in the Santa Monica Mountains, Southern California (Bulletin of the Mineralogical Society of Southern California. Volume 87, Number 8 - August, 2014). In that article he also mentions melanophlogite could be the replaced mineral in the Blue Lace Agate specimens from the Triestia mine in Romania as well as Ysterputs. So perhaps my next step was to see what I could find out about Triestia, and whether its Blue Lace Agate was similar to that of Ysterputs? In so many ways it seems it is.

Ysterputs Blue lace Agate

This is what I found:

Description: A classic, old-time, plate of lustrous, pretty pastel-blue chalcedony pseudomorphs after sharp fluorite cubes from Romania.

Pseudos of this old-time quality are uncommon on the market. Ex Earl Calvert and Robert Whitmore Collections and comes with a faded Anton Berger label, well-known Austrian mineral dealers from the 1920s-1950s. Siebenburgen is a historical region in the central part of Romania.


The Hungarian Natural History Museum has the following specimen and description:

Chalcedony pseudomorphs from Trestia, Transylvania, Romania. Fragment of a blue chalcedony vein with cube-like pseudomorphs in the central cavity.

Chalcedony is the microscopically fibrous variety of quartz. The shown specimen is a piece of a chalcedony vein. Its internal cavity is lined with cube-like crystals, which are actually pseudomorphs: chalcedony filled the empty space of the crystals of an earlier mineral. The original mineral has been debated since two hundred years. This chalcedony has a beautiful blue colour due to Tyndall scattering; it has been used as a gem since the late 1700s. The specimen itself came from the collection of the Esterházy princes, purchased by Andor Semsey for the Hungarian National Museum in 1882.


Likewise from the Romanian Journal of Mineralogy of 1992:

Trestia (Gutii Mts). Occ. type: XII. Celebrated occurrence of the blue chalcedony, known since the 18th century. The sky-blue fragments (5-15 cm in size) are scattered in soil or alluvial material, being formed by solidification of some silica gel originating in hot springs. Sinter-like reniform masses, thin radial-fibrous or parallel banded structures, surfaces imprinted by irregular reliefs or plates and druses inlaid with cubic crystals. Though considered to represent quartz-chalcedony pseudomorphs after fluorite or galena, even a rare species of rhombohedral quartz or a new silica species named "cubosilicite", it is more likely that the blue cubes are quartz-chalcedony paramorphs after melanophlogite. (Rom. J. Mineralogy, 1992, 75, p. 1-51)

It appears that Trestia specimens do have similar-looking pseudomorphs of chalcedony after what is generally called fluorite, and that it has been mined and used as a gem since the late 1700s. SO, THE ORIGINAL MINERAL THAT MIGHT HAVE BEEN REPLACED BY THE CHALCEDONY HAS BEEN DEBATED FOR 250 YEARS! Oh dear, so our thoughts are nothing new, nor is the question I am researching.

What about melanophlogite – is this a newly discovered mineral, as Duncan had never heard of it before either? Nope, according to Wikipedia ( melanophlogite was identified and named by Arnold von Lasaulx in 1876, even though a Mr Alessi had described a similar mineral in 1827. The first studies of melanophlogite were made in Sicily. The mineral was originally called Girghenti after an old Sicilian town, but was officially changed to melanophlogite in 1927, according to The American Mineralogist, Vol. 48, July/August, 1963 (Skinner B.J.; Appleman D.E. (1963). "Melanophlogite, a cubic polymorph of silica" (PDF). American Mineralogist48: 854–867.) I also see that the name melanophlogite describes the fact that the mineral turns black when heated.

And finally to bring me full circle, here are a couple of sentences from the Skinner and Appleman article mentioned immediately above:  “Von Lasaulx described melanophlogite as a cubic form of silica with a hardness of about 6.5 to 7 and a specific gravity of 2.04 at 17.5 °C. Because of the perfection of the cube form of some of his specimens, he suggested that the mineral was pseudomorphous after fluorite or halite.”

This research has proven to be quite a wild gallop over several days, despite following internet links which are much easier to locate now than they were four years ago when I started on the Blue Lace Agate endurance trail. The ride turned into an interesting investigation but has resulted in no clear answers, which is often what happens in scientific enquiries, but it has opened new doors and I have learnt a lot. So, seemingly we are no further in identifying what really went on in the ancient dolerite crack at Ysterputs, some 54 million years ago.

Perhaps we are just phlogging a dead horse?



March 25, 2019

By Peter Rosewarne

Sifting through my collection in order to catalogue and assess specimens more fully has got me thinking more about some of their mineralogical and crystallographic properties. Why are some examples of the same mineral one colour and others another? Why are some stubby and others prismatic? What crystal system do they each belong to? What is ilvaite or axinite or vivianite?

I’m fascinated by the interesting habits that some minerals exhibit which in many cases don’t see...

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February 21, 2019

By Duncan Miller

(This is a follow-up to a previous article on faceting quartz, to be found with other faceting articles on the club’s website 

Every faceter knows quartz, those great big glassy-looking chunks that seem to cry out to be turned into doorknobs. Or pretty, golden ‘citrine’ that can cut brilliant yellow stones. Or glowing, dark purple amethyst with seductive blue flashes, dreamy rose quartz, or rutilated quartz with geom...

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February 21, 2019

By Peter Rosewarne


Having built-up a mineral collection the question arises, at some stage, as to what to do with it looking to the future. Options include do nothing (and continue to get enjoyment out of looking at and handling the specimens) and let someone else worry about it when you’re gone (i.e. throw it away), give it away, donate it to an institution (probably unwise in SA or anywhere probably), or sell it. This article looks at some aspects of the pricing and selling process ba...

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January 19, 2019

By Duncan Miller

Topaz is a rather under-rated gemstone. This perhaps it due to the fact that pure, colourless topaz is relatively plentiful. Much of it is irradiated and then heat-treated to produce various intensities of bright blue. Natural blue topaz tends to be much paler, although dark blue stones do occur naturally. These are rare and hence more valuable. Natural topaz occurs in a wide variety of colours, including light green, yellow, orange and pink. The famous orangey-pink topaz fr...

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Two beached whales were spotted at Yzerfontein this past month, the first on 5th November and the second a few days later

November 23, 2018

And last week this fish appeared at Milnerton Lagoon

Grey chalcedony and aragonite fish

This is the same fish as above, but much prettier “when still alive”, and seen under short wave UV light.

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"There’s treasure – I just have to find it"

November 23, 2018

Talking about treasure hunting, let me tell you my story … It’s a tale of two parts.

I’ve always been the poster child for the story told by Victor Borge:  “if there’s manure, there must be a pony.”  It’s in my DNA.

Truth be told, my first real life encounter with this approach was doomed. 

To understand it better, you’d have to know that back then Dinner, Bed and Breakfast at a swanky hotel cost R40-00 and a full seafood buffet at the same hotel with all you could eat cos...

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FaceTips for December

November 23, 2018
by Duncan Miller

This month I will show you how to scale a GemCad diagram to a different L/W ratio. This is very easy if the diagram is a fully meetpoint diagram, without a preform. You note the initial L/W ratio from the Print Preview and then click on Scale in the Edit menu. Here you check the X box because you want to change the proportions in the X direction, then enter the appropriate numbers to divide by the initial L/W ratio and to multiply by the one you want, and press OK. The next me...

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FaceTips for November

November 4, 2018

By Duncan Miller

I started faceting in pre-GemCad days and found cutting ovals very laborious. I would cut the girdles by eye, using various oval templates, and placed the brilliant-style facets by eye too. Producing matching pairs was very trying. The advent of meetpoint faceting and GemCad overcame all these difficulties. Now there are lots of designs for ovals that are meetpoint, requiring no preform, with the girdle outline evolving out of the cutting sequence. You can access some of the...

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October 25, 2018

The Waldorf School asked us if they could visit the club again this year, and Claire Vaskys organised the day for them. Thank you very much Claire.

Also a big thank you to Rinda who had kept all the little offcuts of stones, and dopped them in preparation for the children to grind and polish, and who managed the workshop while they were busy between machines. 

Thank you to Marsiglio who brought his tools, raw and finished materials, and allowed the kids to take his rock pick and smash it in...

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