Acta Musei Moraviae

Mineralogy of glauconitic sandstone, wastes from its processing and glass sand from Dolní Lhota near Blansko

In Dolní Lhota near Blansko (Czech Republic), the decaying sandstones of the Bohemian Cretaceous Basin, formerly used as a raw material for the production of foundry sand, are currently being processed into construction sand, used mainly as a filler in building materials. From the petrographic point of view, two types of sandstones are mined here: (i) quartz sandstone with a transition to quartz conglomerate (considered as freshwater sandstone) with a SiO2 content of about 96 wt. %, (ii) glauconitic quartz sandstone (marine) with a glauconite content of up to about 20 % by volume. Glauconitic quartz sandstone has a relatively high content of Al₂O₃ (on average 6.2 wt. %), Fe₂O₃ (4.5 wt.%) and K₂O (2.5 wt.%), The main carrier of all three oxides is glauconite. In addition to quartz and glauconite, feldspars (alkali and plagioclase), clastic muscovite, altered mafic minerals, kaolinite, illite, rutile, leucoxene, zircon, monazite-(Ce), ilmenite, magnetite, garnet and other accessory minerals are involved in the composition of sand – stones. The glauconitic quartz sandstone locally contains abundant limonite concretions. Glauconite contains an average of about 8.0 wt. % K₂O. It can therefore be assumed that it is a glauconite with an ordered structure, containing less than 10% of smectite layers. Processed glass sand obtained from the raw material mined in the Dolní Lhota quarry on a laboratory and model scale meets the parameters for being used, for example, in the production of green or brown container glass. Coarse grain fractions could, after further refining, meet even more demanding criteria for the production of white container or sheet glass. Waste from the production of construction sand is a water-washable fraction deposited in sludge ponds. This waste could be used to produce glauconite concentrate by magnetic separation. Monomineral glauconite concentrates are used, for example, in the pharmaceutical and cosmetic industries. Lower purity glauconite concentrates (glauconite rich fine-grained sands) can be marketed as potassium fertilizer and soil conditioner.