Lublinite: Needle Form Calcite

Needle form calcite ("Lublinite") XRDs as calcite however a casual glance reminds one of aragonite as it takes an acicular form. It is usually associated with soil bacteria, however it has "popped up" in an interesting form: as ribbon helictites. See "Cataloguing Helictites and other capillary-controlled speleothems".

With a suitable polarising filter, under an optical microscope the needle fibres may be seen. It is a rod of calcite, where each calcite rhomb is attached en echelon to the neighbouring rhomb. Sketch of lublinite lath

Calcite does not normally precipitate in this form with inorganic processes, however is is a fairly common form when associated with microorganisms (eg Philips and Self, 1987, and also Moore and Sullivan).

Philips and Self (1987) showed several forms of lublinite, some including an organic coating. Possibly organic material holds the shape of the laths, preventing them from coalescing.

Needle Form Calcite in Wollondilly Cave

As part of the cave aragonite project (Rowling, 2004b), I found needle form calcite in fluffy material from "The Loft", Wollondilly Cave (Wombeyan Caves, NSW). The fluffy material also included sediment grains. The area appeared to have had a bat guano deposit a long time ago. The needle fibres were easily visible with a microscope, and the whole material resembled a thatch.
Samples were prepared for viewing with an electron microscope, a Phillips SEM 505 at the University of Sydney Electron Microscope Unit. The results are shown below.
Details of the setup are in Rowling, 2004b.

The material was examined with XRD and grouped into major, minor and trace according to the apparent quantity of material present in the sample. In the list below, the "major" and "minor" mineral constituents are reasonably accurate; the trace components however should be taken with a grain of salt as there may be other substances which exhibit similar spectra. It would be better to further test the material (e.g. with mass spectrometry) before one could say for sure that the trace minerals were actually present. XRD scans took about 20 minutes per specimen, and subsequent spectral analysis took about 20 to 30 minutes per specimen, using the software.
The instruments used were a Siemens Kristalloflex 710D X-Ray generator and D5000 Diffractometer, at the Electron Microscope Unit at the University of Sydney. Details are in Rowling, 2004b.

Sample ID W144/5 minerals detected using XRD
This was the most fluffy white material with the longest fibres.
Possibly the aragonite is derived from vaterite.
Suggested mineral originMajorMinorTrace
Detrital quartzajoite

Sample ID W144/11 minerals detected using XRD
This was the more yellow material with the shorter fibres.
Suggested mineral originMajorMinorTrace
Detritalquartz ajoite

Sample ID W144/12 minerals detected using XRD
This was the gravel substrate to the fluffy material.
Suggested mineral originMajorMinorTrace
Cavecalcitearagonitemagnesian calcite
  heneuitesodian meionite
  manganoan calcitetilleyite
Detritalquartz aerinite
   high quartz

Some of these may be formed by the action of bat guano on sediments, and others may be derived from reactions with the showcave wire netting. Some minerals are hydrated forms of more common cave minerals. The detrital material appears to be derived from the surrounding volcanics.

The white fluffy material (W144/5 and W144/10) is mainly composed of needle fibre rods, about 1 x 2 μm thick and from 10 μm up to about 1 or 2 mm long. The rods are rectangular with chamfered or 90 ˆ terminations. The material also contains irregular blobs about 2 to 5 μm diameter. The yellow and pale orange material is a mixture of shorter, wider needle fibre rods, along with quartz and other crystal grains and irregular shapes. The yellow material has more needle fibre calcite than the pale orange material which has a higher quantity of quartz and clays. Terminations to the needle fibres are either rectangular or pointed. Some quartz crystal grains are coated in the short fibres.

Electron Micrographs of Wollondilly Cave Needle Form Calcite

White fluffy material: sample W144/10.
100kb jpg image Needle form calcite, sample ID W144/10 The white fluffy needle form calcite resembles a thatch.
60kb jpg image Needle form calcite, sample ID W144/10 Looking closer, the material is very light, with plenty of space between the laths.
Yellow fluffy material: sample W144/11.
121kb jpg image Needle form calcite, sample ID W144/11 Sample W144/11 piece 2 on disc: yellow fluffy material is more dense and has shorter fibres than the white material.
89kb jpg image Needle form calcite, sample ID W144/11 Close-in view of sample W144/11, piece 2 on disc, showing termination types of short fibres. Although there are some long fibres, many fibres are not straight; some are bent and joined with others. This thatch looks more "glued together". Some terminations are square (like W144/10) whereas others are pointed.
122kb jpg image Needle form calcite, sample ID W144/10 Looking a bit closer at the thatch of sample W144/11, piece 3 on disc. This shows the shorter needle fibres and a spheroidal aggregate (possibly a quartz grain). with some fibres apparently "glued" to others.
109kb jpg image Needle form calcite, sample ID W144/11 Close-in view of sample showing termination types of short fibres. Some fibres resemble those in Folk, Chafetz & Tiezzi, 1985 (from bacterial shrubs). Some terminations are square (like W144/10) whereas others are pointed. The ones in the picture vaguely resemble en-echelon calcite. Diameter of laths varies from about 1 μm to 2 μm. Some of these fibres vaguely resemble en-echelon calcite.
90kb jpg image Needle form calcite, sample ID W144/11 This is a closer view of the substrate for the "yellow fluffy stuff". The larger grains are probably quartz and there may be clays, mica, feldspar etc. One needle fibre is visible. There is a lot of charging here, possibly from a lack of conductive coating on areas of clay.

Needle Form Calcite and Ribbon Helictites

Surface of ribbon helictite exhibits laths
Lublinite-like laths are visible with the electron microscope. The picture is a portion of the surface of a ribbon helictite. Scale bar is 0,1 mm.
A cropped version of this photo appeared in Rowling, J. (1998) "Ribbon Helictites: A New Category" Helictite 36(1) 2-10.
The electron micrograph and sample preparation is by Terry Furey-Grieg, University of Technology, Sydney.
Electron micrograph of ribbon helictite lath

Cosmetic update, January 2006. Content created 4th February 2001 and updated 7th February 2006.

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