Diatomites and spon­go­lites. Gen­e­sis, prop­er­ties, and indus­tri­al sig­nif­i­cance

Diatomites and spon­go­lites have a lot in com­mon. Both rocks are of sed­i­men­ta­ry ori­gin and con­tain sig­nif­i­cant amounts of sil­i­ca, although the sources of this sil­i­ca are dif­fer­ent. Diatomites are formed from the opal shells of diatom algae, while spon­go­lites are formed from the spicules of siliceous sponges. Both rocks are char­ac­ter­ized by high poros­i­ty and low bulk den­si­ty, which makes them valu­able in indus­try, par­tic­u­lar­ly in cement pro­duc­tion. They are used as active min­er­al addi­tives to improve the qual­i­ty of cement, in par­tic­u­lar to elim­i­nate the harm­ful effects of cal­ci­um oxide hydrate.

Diatomites and spon­go­lites are includ­ed in the list of min­er­als of nation­al impor­tance approved by Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine No. 827 of Decem­ber 12, 1994, as adsorp­tion raw mate­ri­als and cement raw mate­ri­als.

Physical and chemical properties

Diatomites and spon­go­lites have a num­ber of sim­i­lar and dif­fer­ent phys­i­cal and chem­i­cal prop­er­ties, which deter­mine their areas of appli­ca­tion, espe­cial­ly in the cement indus­try.

Diatomites are very light and porous due to their struc­ture con­sist­ing of diatom algae shells. They have low bulk den­si­ty, good adsorp­tion capac­i­ty, and ther­mal insu­la­tion char­ac­ter­is­tics. How­ev­er, the ther­mal sta­bil­i­ty of diatomites is lim­it­ed due to the insta­bil­i­ty of their struc­ture at high tem­per­a­tures. The main active com­po­nent of diatomites is amor­phous opal, which can eas­i­ly under­go struc­tur­al changes when heat­ed. Chem­i­cal­ly, they are rel­a­tive­ly inert but have low resis­tance to acids.

Spono­liths, on the oth­er hand, demon­strate bet­ter ther­mal sta­bil­i­ty prop­er­ties due to their high con­tent of active sil­i­ca in the form of opal and spicule sil­i­con sponges, which some­times trans­form into more sta­ble forms, such as chal­cedony. Thanks to this, spono­liths do not lose their prop­er­ties even when heat­ed sig­nif­i­cant­ly. They also have very high chem­i­cal resis­tance to acids, which makes them valu­able in aggres­sive envi­ron­ments. In addi­tion, spon­go­lites can effec­tive­ly inter­act with cal­ci­um com­pounds, in par­tic­u­lar by con­vert­ing cal­ci­um oxide hydrate into poor­ly sol­u­ble cal­ci­um hydrosil­i­cates. This con­tributes to the increased dura­bil­i­ty of cemen­ti­tious mate­ri­als.

Both types of rock have high poros­i­ty, which ensures low ther­mal con­duc­tiv­i­ty and good fil­tra­tion prop­er­ties. It is thanks to these char­ac­ter­is­tics that diatomites and spon­go­lites are wide­ly used as addi­tives to improve strength, reduce crack­ing, and increase the resis­tance of cement struc­tures to exter­nal influ­ences.

Genesis

Diatomites and spon­go­lites are sed­i­men­ta­ry rocks of bio­genic ori­gin that were formed in marine and coastal envi­ron­ments. The main source of sil­i­ca for both rocks was the remains of organ­isms rich in sil­i­con. The process of their for­ma­tion involved the accu­mu­la­tion of bio­log­i­cal remains (shells of diatom algae or spicules of siliceous sponges) at the bot­tom of water bod­ies. Over time, these deposits were com­pact­ed under the pres­sure of the upper lay­ers of sed­i­ments and under­went dia­ge­net­ic changes. Such con­di­tions con­tributed to the preser­va­tion of high poros­i­ty of both rocks and their main com­po­nent – amor­phous sil­i­ca.

How­ev­er, there are dif­fer­ences in the gen­e­sis of these rocks. Diatomites were formed in fresh­wa­ter and marine basins from the shells of diatom algae mea­sur­ing 0.01–0.04 mm, com­posed of amor­phous opal. They were formed in a wide strati­graph­ic range – from the Cre­ta­ceous to the Neo­gene epochs.

Spono­liths, on the oth­er hand, orig­i­nat­ed exclu­sive­ly in marine envi­ron­ments from the remains of siliceous sponges (sponges), whose skele­tons con­sist­ed of spicules of opal struc­ture, some­times tran­si­tion­ing into chal­cedony. These rocks began to form in the Cre­ta­ceous peri­od and are most com­mon in Ceno­zoic coastal marine deposits, char­ac­ter­ized by greater ther­mal and chem­i­cal sta­bil­i­ty.

Distribution in Ukraine

Deposits of diatomites and spon­go­lites occur in the same regions of Ukraine, in par­tic­u­lar in Don­bas, the Azov megablock, the Black Sea and Lviv basins, as well as in the Moun­tain­ous Crimea. How­ev­er, they dif­fer in terms of geo­log­i­cal stratig­ra­phy. Diatomites are main­ly asso­ci­at­ed with deposits from the Cre­ta­ceous, Pale­o­gene, and Neo­gene peri­ods, while spon­go­lites are also known from Cre­ta­ceous deposits, but are most wide­spread in Ceno­zoic marine deposits.

Accord­ing to the State Bal­ance of Min­er­al Reserves of Ukraine, only one diatomite deposit and one spon­go­lite deposit are record­ed.

The Velykoburlut­skoye deposit of diatomites is locat­ed in the dis­trict of the same name in the Kharkiv region, 1 km north­east of the vil­lage of Hni­lyt­sia and 7 km north­east of the Burluk rail­way sta­tion. The diatomite lay­er in this deposit has a thick­ness of 0.5 to 14.5 m and extends for a dis­tance of 3.2 km. Total con­firmed reserves, which are used as an active min­er­al addi­tive in the cement indus­try, exceed 11 mil­lion tons.

Rava-Rus­ka deposit of spon­go­lites, locat­ed in the Zhovkivsky dis­trict of the Lviv region, on the east­ern out­skirts of the vil­lage of Pote­lych, 4–5 km south­west of the Rava-Rus­ka rail­way sta­tion. Here, spon­go­lites form two deposits with a thick­ness of 1.2 to 35 m among lime­stones and clayey marls of the Cre­ta­ceous age. The con­firmed reserves of the deposit amount to 23.391 mil­lion tons.

Use of diatomites and spongolites

Diatomites and spon­go­lites are wide­ly used in indus­try, espe­cial­ly in cement pro­duc­tion. Due to their high poros­i­ty and light­ness, diatomites serve as an active min­er­al addi­tive that improves the struc­ture of cement and reduces crack­ing. They are also used in fil­tra­tion sys­tems, as a heat-insu­lat­ing mate­r­i­al, and as an adsor­bent for puri­fy­ing liq­uids and gas­es.

Sponge stones, in turn, due to their high ther­mal sta­bil­i­ty, chem­i­cal resis­tance to acids, and sig­nif­i­cant poros­i­ty, are also impor­tant addi­tives in cement pro­duc­tion. They neu­tral­ize cal­ci­um oxide hydrate, increas­ing the dura­bil­i­ty and strength of con­crete struc­tures. In addi­tion to the cement indus­try, spon­go­lites are used in the pro­duc­tion of refrac­to­ry mate­ri­als, chem­i­cal fil­ters, and ther­mal insu­la­tion that oper­ates in high tem­per­a­tures and aggres­sive envi­ron­ments.