Vermiculite formula

The Na+- and Ca2+-saturated montmorilIonite, saponite and beidel-lite were obtained from Dr. J. L. McAtee, Chemistry Department, Baylor University. These minerals had been purified and prepared by methods described by Callaway and McAtee (15). Included in this paper for purposes of comparison are relevant data from previous studies in which hectorite and vermiculite had been doped with paramagnetic probes ( 7, 10). The chemical formulae of the low-Fe smectites and mermiculite are reported in Table I. 

Partial structural formulas for some vermiculites (selected from Foster, 1963)... 

Structural formulas for vermiculite clays (After Barshad and Kishk, 1969)... 

As indicated in Table 1, the three 2 1 groups differ from one another in two principal ways. The layer charge decreases in the order illite > vermiculite > smectite, and the vermiculite group is further distinguished from the smectite group by the extent of isomorphic substitution in the tetrahedral sheets. Among the smectites, those in which substitution of Al for Si exceeds that of Fe2+ or Mg for Al are called beidellite, and those in which the reverse is true are called montmorillonite. The sample chemical formula in Table 1 for smectite thus represents montmorillonite. In any of these 2 1 clay... 

I was lucky to receive some jars of sodium-substituted Eucatex vermiculite and n-butylammonium-substituted Eucatex vermiculite. These synthetic systems had been obtained by cation exchange on the raw minerals. Such cation exchange plays a major role in clay chemistry, and the process is described in detail in standard books on clay colloids, like that of van Olphen [2], Some years later, I was able to obtain the following chemical formula for the dry sodium Eucatex vermiculite [3]... 

This is a typical formula for a vermiculite. If we put all the elements in their formal oxidation states, the condition for charge neutrality of the mineral is satisfied if the transition metal elements are in their higher oxidation states. 

As we wanted to make a complete structural determination of the mineral, we used a more highly oriented vermiculite from Llano, Texas. This was a special clay (VTx-1) from the Clay Minerals Society s Source Clays Repository it had the structural formula [23]... 

To estimate the degree of polymer adsorption, we first calculate the total layer surface area of the vermiculite in the crystalline state. The formula for the dry sodium Eucatex sample considered in Chapter 1 can be abbreviated as... 

I strongly recommend that you grow your plants in my standard medium formula /, perlite, /, vermiculite and /, potting soil. This combination of ingredients as your hydroponic medium holds the nutrients and facilitates the upward capillary action of the water delivered from the resen/oir. 

The plants in the container will then develop two separate root systems. The upper root system will use any hydroponic medium you wish other than lava rock, which is used on the bottom half. I recommend that you use rockwool, coconut fiber, composted bark, Oasis fiber, peat perlite, and vermiculite, or my standard suggested "soil" formula for the upper medium layer. You may use... 

A reference book lists the chemical formula of one form of vermiculite as... 

Note Cations listed first in curved brackets for the smectites and vermiculites (Na, Ca, K, and Mg) arc present as exchangeable interlayer ions. All the smectites and vermiculites (and thus interlayer iilite-smectites) have important amounts of interlayer water, the amount of which depends upon the clay and the nature of interlayer cations (cf. Brindley and Brown 1980). As is customary, these waters are left out of the mineral formulae. 

In these formulas, X denotes a monovalent cation such as Na" and/or Ca ", occupying interlayer exchange sites. The formulas show that beidellite is magnesium-free and montmorillonite magnesium-rich. Other smectite minerals include nontronite, hectorite, saponite, and sauconite (Table 9.1). All the smectites (and vermiculites) have swelling properties. 

Be able to calculate the ion exchange capacity of a smectite or vermiculite clay (meq/100 g clay) from the chemical formula of the clay. 

A vermiculite clay has the structural formula K.Mgo.sKMgaoFe sFeJ sXAl, sSi65)02o(OH)4. Calculate its cation-exchange capacity in meq/IOO g and its surface-site density in mol/g. Assuming the surface area of the clay is 30 mVg, what is its surface-site density in nm and /umol/m ... 

The primary mineral, chlorite, which occurs in rocks as large crystals, possesses an interlayer sheet composed largely of Mg(OH)2. Since the mineral brucite is composed of magnesia sheets with the same basic structure, the single interlayer sheet in chlorite is termed the brucite layer. Isomorphous substitution of part of the Mg by produces a positively chained hydroxide sheet (see formula above) that props the 2 1 layers apart at a c-spacing of 14 A. This rigid interlayer contrasts with the hydrated interlayer of vermiculite, and even though chlorite and vermiculite have similar c-... 

Micas lose their structural relatively rapidly by a process of cation exchange with or metal ions in the weathering solution. This initial reaction is an alteration that is not necessarily very sensitive to pH. The pH, however, tends to rise during alteration as H" is adsorbed. The secondary mineral formed directly is a vermiculite, which inherits more or less intact the 2 1 layer structure of the mica parent. An ideal biotite mica might have the formula ... 

Typical results of specific surface area determinations on phyllosilicates by nitrogen gas/water vapor or nitrogen gas/CPB adsorption are listed in Table 1.7. For Mg-vermiculite and Na-montmorillonite, the measured adsorption specific surface area is close to that calculated from the unit cell dimensions and structural formula. For illitic mica, the area is about 14 per cent of the ideal crystallographic value, indicating that this mineral forms particles containing about seven phyllosilicate layers that cannot be penetrated by water vapor or CPB. 

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