AP42 Section: 11.22 Reference: 2 Title: F. L. Kadey, "Diatomite", Industrial Rocks And Minerals, Volume I, Society Of Mining Engineers, New York, 1983. 1976, "The :ameters On mond Bits .. PP. 82-89. Diatomite use Of.Dio. P: 166. "Abundance FREDERIC L. KADEY. JR.* 21. 157, No. des of Dia. ha (Johan. 5-9. nd AppIita. .ME Preprint ' York, 8 pp, oesticide extender to name a few representative esis." Indar. Diatomite is a siliceous, sedimentary rock -199. consisting principally of the fossilized skeletal applications. 1961, "The remains of the diatom, a unicellular aquatic The United States is the principal producing AsIrouhysics plant related lo the algae. Thus, it has been country, although diatomite'is foind In numer- ous other locations. ~ formed by the induration of diatomaceous ooze, 5 Mechanical - and consists mainly of diatomaceous silica, a I Diamonds," .. form or variety of opal which is first formed Geology in the cell walls of the living diatom. Dia- he Diomond, j tomaceous silica is not generally regarded as a Composition and Morphology ' synonym ' or the equivalent for diatomite, although it has been so used at various times. Diatomaceous silica qualifies as a mineral Of Accurately, diatomaceous silica is the preferred organic origin in much the same way that name for the principal mineral component of. aragonite and collophane do. The silica of the which the rock, diatomite, is composed. The fossilized diatom skeleton closely resembles terms diatomaceous earth and kieselguhr are opal or hydrous silica in composition used as synonymous with diatomite. The desig- (SiO;nH,O).". The silica is of acute nations tripoli, tripolite, infusorial earth, etc., biological significance, not only for the cell wall _. were used at one time but are now obsolete. component, but also for the hasic life pro- With the changing nomenclature, these terms cess.16. Without silica, cell development that were at one time correct when proposed ceases."' In addition to bound water, varying and used for generations would he considered between 3.5 and 8%, the siliceous skeleton may incorrect if used today in the light of current also contain, in solid solution, or as part of the knowledge. The designation diatomite is re- SiO, complex, small amounts of associated in- ' served for those accumulations of diatoma- organic components-alumina, principally- ceous silica that are of sufficient quality, size, and lesser amounts of iron,'c, m alkaline I and minability to be considered of potential earths, alkali metals, and other minor consti- 7 commercial value. tuents."g. 6i Boron is reported to be an essen- :' Processed diatomite possesses an unusual tial element for diatom growth.", Since j particulate structure and chemical stability that diatomaceous silica is not pure hydrous silica lends itself to applications not filled by any hut contains other intimately associated ele- other form of silica. Foremost among these ments, there is good reason to consider it a applications is its use"as a filter aid, which distinct type or variety.' Associated with the accounts for over half of its current consump- diatomaceous silica, and integrated as part of tion. Its unique diatom structure, low bulk the diatomite, may he variable amounts of organic matter, soluble salts, and particles of density, high absorptive capacity, high surface rock-forming minerals that were syngenetically area, and relatively low abrasion are attributes deposited or precipitated with the diatom frus- responsible for its utility as a functional filler tules. Sand, clay, carbonate, and volcanic ash and as an extender in paint, paper, rubber, and are typical common contaminants. Other con- in plastics; and as an anti-caking agent; thermal taminating minerals may be present, such as insulating material; catalyst carrier; and chro- feldspar, mica, amphiboles, pyroxenes, rutile, matographic support; polish, abrasive, and zircon-the result of weathering, then trans- -. porting, and subsequent redeposition of sur- - * Exploration Manager. Manville International rounding land masses, Commercial diatomite Corp.. Denver, CO. may also contain fragments and particles of 678 Industrial Minerals and Rocks .. other such organisms as silico-flagellates, radio- consistent and orderly design (Figs. 1-3). laria and siliceous sponges, Furthermore, each valve appears to consist of In a commercial diatomite. silica makes up an inner and an outer platelike surface, sepa- the bulk of the chemical composition: usually rated by ribs that result in a chambered inte- over 86% and as high as 94%. Alumina and rior. The structure of each surface is different iron generally are at least 1.5 and 0.2%. re- in that the nature of the openings from each spectively. This includes not only that believed surface into the chamber is not necessarily the to be incorporated as part of the skeleton but same. It is on the basis of the' valve structure iron and alumina associated with many of the that diatoms are classified. The openings in the . ' contaminants. Lesser amounts of other ele- skeleton, classified by diatomists and divided ments, a small part of which may be secreted into primary, secondary, and in some species, in the diatom skeleton, comprise the balance tertiary structures, are believed to simply sup:.& of the total chemical composition. The manner port the membrane of the living diatom through ,, in which many of these elements are associated which the nutrients pass by the process of os- .#- ! is not presently known. Table 1 illustrates the mosis. The valves vary between approximately jr e chemical composition of diatomites from vari- 5 and IOOOp in diameter, or maximum dimen-, ' ous areas.' Although diatoms appear amor- sion, depending on the genus (Fig. 4). Most . phous under the light microscope, X-ray studies species fall within the range of 50 to lSOp, Itl show untreated diatomite to have a broad halo is not within the scope of this chapter to dwell in the region of the principal cristobalite peak, further on the botanical aspects of the diatom, thus it has been referred to as "micro- although a few of the numerous references on amorphous." & The main X-ray line is an ap- the subject are included in the bibliography for proximation and not identical with a-cristo- the interested reader. , .. balite.6G Some researchers have reported Suffice it to say that outside the realm of 8-cristobalite to be prevalent." The crystalline mining and commerce, the diatom has its own impurities produce their own X-ray lines; hence nomenclature and scientific entity, the study of they furnish an identification of their nature, to which distinguishes it as a source of enjoyment a greater or lesser degree, depending on the for amateur and professional microscopists amounts present. The ultimate hardness of the alike: and as a scientific tool in the fields of diatom skeleton is between 4'h and 5 on the limnology, stratigraphic correlation, and other Mohs' scale. After calcination or flux calcina- similar noncommercial applications.3. 7s. 82, 85* . tion. the Mohs' hardness is increased to 5% to 'N Certain properties of diatomite-physical . 6. The friability, or the propensity of the and chemical-may be visualized as primary or ' . skeleton to break down, rather than to abrade, fundamental in nature. The nature and con- renders a measurement of hardness meaningless figuration of the skeletal structure, specific without also a consideration of the particle gravity, refractive index, hardness and fri- '. size."* The specific gravity ranges from 1.95 ability, and composition are a few. These are. to 2.3. In calculating settling velocities, bulking the properties that determine secondary or de- values, etc., an apparent specific gravity of 2.0 rived properties which also endow diatomite for natural milled powders and of 2.3 for flux with the attributes that set it apart from other calcined powders is generally used.'J' Refrac- sources of silica. It is an accurate generaliza- tive index is variable between about 1.40 and tion to state that the skeletal structure or con- ' . 1.46 for natural earth, and increases to 1.49 figuration of the diatom is the principal primary for flux calcined diatomite. property that controls most of the derived or Taxonomically, diatoms are divided into two secondary properties. Low bulk density, low . broad categories: Centricae (discoid) and Pen- wet or cake density, and high surface area may natae (elongate to filiform). The study of the be visualized as examples of derived or sec- various intricate shapes and structural patterns ondary properties. The loose weight and wet of individual siliceous skeletons is as old as the density, for example, are a function of, and use of the light microscope itself. Each form depend on, the skeletal Structure and specific consists of two valves that are bound together gravity. The particle size and shape on which by a connecting band or girdle. In the living bulk and wet cake density depend can be altered diatom, these encase the cell contents. to a degree by milling: but ultimately, they are Each siliceous valve is punctated by a system determined by such primary propertiff as strnc- - or pattern of openings that are arranged in a ture, density, and friability. Certain properties - h Diatomite 679 . 1-3). 3(oLnOOO~(oO* Insist of lL?Yl7NTqYlO)II)? O--000P00~ :e, sepa. r 'ed inte. different im each lrily the tructure rs in the divided: species, PIY sup- through s of os- cimately dirnen. 8. Most so,. It 10 dwell diatom, nces on .phy for :ah of its own tudy of oyment scopists elds of- d other 5. B?. *5, physical nary or .d con- specific id fri- ese are or de- itomite L other :raliza- c con- rimary red or f3 . low a may 'r sec- d wet i, and pecific which :Itered 3y are struc- wties Diatomite 681 ..