A number of mineral species were exposed to martian surface conditions of atmospheric pressure and composition, temperature, and UV light regime, and their evolution was monitored using reflectance ...spectroscopy. The stabilities for different groups varied widely. Phyllosilicate spectra all showed measurable losses of interlayer H
2O, with some structural groups showing more rapid H
2O loss than others. Loss of OH from the phyllosilicates is not always accompanied by a change in metal–OH overtone absorption bands. OH-bearing sulfates, such as jarosite and alunite, show no measurable change in spectral properties, suggesting that they should be spectrally detectable on Mars on the basis of diagnostic absorption bands in the 0.4–2.5 μm region. Fe
3+- and H
2O-bearing sulfates all showed changes in the appearance and/or reduction in depths of hydroxo-bridged Fe
3+ absorption bands, particularly at 0.43 μm. The spectral changes were often accompanied by visible color changes, suggesting that subsurface sulfates exposed to the martian surface environment may undergo measurable changes in reflectance spectra and color over short periods of time (days to weeks). Organic-bearing geological materials showed no measurable change in C
H related absorption bands, while carbonates and hydroxides also showed no systematic changes in spectral properties. The addition of ultraviolet irradiation did not seem to affect mineral stability or rate of spectral change, with one exception (hexahydrite). In some cases, spectral changes could be related to the formation of specific new phases. The data also suggest that hydrated minerals detected on Mars to date retain their diagnostic spectral properties that allow their unique identification.
Complex rotator cuff tears provide a significant challenge for treating surgeons, given their high failure rate following repair and the associated morbidity. The purpose of this study is to evaluate ...the clinical outcomes of patients who underwent biologically enhanced demineralized bone matrix augmentation of rotator cuff repairs. Twenty patients with complex rotator cuff tears underwent arthroscopic rotator cuff repair by a single surgeon with demineralized bone matrix (DBM) augmentation that was biologically enhanced with platelet-rich plasma and concentrated bone marrow aspirate. Post-operative MRI was used to determine surgical success. Patient reported outcome measures and range of motion data were collected pre-operatively and at the final post-operative visit for each patient. Ten patients (50%) with DBM augmentation of their arthroscopic rotator cuff repair were deemed non-failures. The failure group had less improvement of visual analogue pain scale (
= 0.017), Simple Shoulder Test (
= 0.032), Single Assessment Numerical Evaluation (
= 0.006) and abduction (
= 0.046). There was no difference between the groups for change in American Shoulder and Elbow Society score (
= 0.096), Constant-Murley score (
= 0.086), forward elevation (
= 0.191) or external rotation (
= 0.333). The present study found that 50% of patients who underwent biologically enhanced DBM augmentation of their rotator cuff repair demonstrated MRI-determined failure of supraspinatus healing.
The crystal structure of dixenite, ideally Cu+Fe3+Mn142+(As5+O4)(As3+O3)5(SiO4)2(OH)6, from Langban, Sweden, was refined to an R1-index of 1.58%, and the structure proposed by Araki and Moore (1981) ...was confirmed and details elucidated. The structure, crystallizing in space group R3 with a=8.2204(3) and c=37.485(3) Å, consists of layers of (Mn2+,Fe3+)(O,OH)6 octahedra linked by (As5+O4) and (SiO4) tetrahedra, (As3+O3) trigonal pyramids, and (CU+As43+) tetrahedra. There are five distinct layers in the repeat unit of the cell, four of which are very similar to the layers in mcgovernite. An unusual aspect of one of the trimers of octahedra is that there is a triangular-prismatic hole through the center of the cluster. The (CU+As43+) tetrahedra are parts of larger clusters: Cu+(As3+O3)4 in which four (As3+O3) groups link to a central Cu+ that occupies the positions normally taken by the stereoactive lone-pairs of electrons that generally characterize As3+ in triangular-pyramidal coordination by O. Thus, the stereoactive lone-pair behavior that is characteristic of (As3+O3) trigonal pyramids is suppressed by the coordination of Cu+ by four As3+ ions.
The crystal structure of a mineral may be divided into two parts: (1) the
, an array of high-bond-valence polyhedra that is usually anionic in character, and (2) the
, an array of large low-valence ...cations, simple anions and (H
O) groups that is usually cationic in character. Interstitial complexes link the structural units with weak cation-anion and hydrogen bonds into a continuous structure, and the breakdown of a structure is usually controlled by the strengths of the weak bonds that link the structural units together. The interstitial complex is (usually) a complex cation, and can be characterized by its
, a measure of the electrophilic character of the complex. The structural unit is (usually) a complex oxyanion, and can be characterized by its
. The interaction between the structural unit and the interstitial complex can be examined using the
. If one examines a series of structures with the same structural unit, it is evident that the average coordination of the O atoms of the structural unit varies slightly from one structure to another, producing a range of Lewis basicity for this specific structural unit. In this way, a specific structural unit can be stable over a range of Lewis basicity (
over a specific pH range). The formula of an interstitial complex may be written in the following way: {
·
(H
O)
(H
O)
(OH)
(H
O)
, where
,
and
are coordination numbers,
and
are the numbers of monovalent, divalent and trivalent cations,
is the number of
(H
O) groups,
is the number of (H
O) groups bonded to two interstitial cations or one interstitial cation and one hydrogen bond,
is the number of interstitial (OH) groups, and
is the number of (H
O) groups not bonded to any cation. The number of transformer (H
O) groups strongly affects the Lewis acidity of the interstitial complex, and the variation in Lewis acidity of a generalized interstitial complex can be graphically represented as a function of the number of transformer (H
O) groups. Where the Lewis acidity of a generalized interstitial complex overlaps the range of Lewis basicity of a specific structural unit, the principle of correspondence of Lewis acidity-basicity is satisfied and a stable structural arrangement is possible. Detailed predictions of the compositions of interstitial complexes are made for the borate, sulfate and uranyl-oxide-hydroxy-hydrate minerals. There is fairly close agreement between the predicted ranges of interstitial complex and those observed in Nature.
Fluor-elbaite, Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3F, is a new mineral of the tourmaline supergroup. It is found in miarolitic cavities in association with quartz, pink muscovite, lepidolite, ...spodumene, spessartine, and pink beryl in the Cruzeiro and Urubu mines (Minas Gerais, Brazil), and apparently formed from late-stage hydrothermal solutions related to the granitic pegmatite. Crystals are blue-green with a vitreous luster, sub-conchoidal fracture and white streak. Fluor-elbaite has a Mohs hardness of approximately 7.5, and has a calculated density of about 3.1 g/cm3. In plane-polarized light, fluor-elbaite is pleochroic (O = green/bluish green, E = pale green), uniaxial negative. Fluor-elbaite is rhombohedral, space group R3m, a = 15.8933(2), c = 7.1222(1) Å, V = 1558.02(4) Å3, Z = 3 (for the Cruzeiro material). The strongest eight X-ray-diffraction lines in the powder pattern d in Å(I)(hkl) are: 2.568(100)(051), 2.939(92)(122), 3.447(67)(012), 3.974(58)(220), 2.031(57)(152), 4.200(49)(211), 1.444(32)(642), and 1.650(31)(063). Analysis by a combination of electron microprobe, secondary ion mass spectrometry, and Mossbauer spectroscopy gives SiO2 = 37.48, Al2O3 = 37.81, FeO = 3.39, MnO = 2.09, ZnO = 0.27, CaO = 0.34, Na2O = 2.51, K2O = 0.06, F = 1.49, B2O3 = 10.83, Li2O = 1.58, H2O = 3.03, sum 100.25 wt%. The unit formula is: X(Na0.780.15Ca0.06K0.01)Y(Al1.15 Li1.02Fe2+0.46Mn2+0.28Zn0.03) ZAl6T(Si6.02O18)B(BO3)3V(OH)3W(F0.76OH 024). The crystal structure of fluor-elbaite was refined to statistical indices R1 for all reflections less then 2% using MoKα X-ray intensity data. Fluor-elbaite shows relations with elbaite and tsilaisite through the substitutions WF ⇌ WOH and Y(Al + Li) + WF ⇌ 2YMn2+ + WOH, respectively.
The classification and nomenclature of mineral species is regulated by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA-CNMNC). This ...mineral species classification is necessary for Earth Sciences, as minerals constitute most planetary and interstellar materials.
has proposed a classification of minerals and other Earth and planetary materials according to “natural clustering.” Although this classification is complementary to the IMA-CNMNC mineral classification and is described as such, there are some unjustified criticisms and factual errors in the comparison of the two schemes. It is the intent of the present comment to (1) clarify the use of classification schemes for Earth and planetary materials, and (2) counter erroneous criticisms or statements about the current IMA-CNMNC system of approving proposals for new mineral species and classifications.
PDF
