Meyerhofferite

Meyerhofferite is a hydrated calcium borate with the formula CaB₃O₃(OH)₅·H₂O and a molar mass of 223.56 g/mol.迈耶霍夫石是水合硼酸钙，化学式为 CaB₃O₃(OH)₅·H₂O，摩尔质量 223.56 g/mol。

It is best known as an alteration product of inyoite in sedimentary and lacustrine borate deposits, where it is a minor constituent of the ore rather than an ore mineral in its own right.它最知名之处是作为沉积与湖相硼酸盐矿床中因水硼钙石的蚀变产物，在矿石中只属次要组分，本身并非矿石矿物。

The species is triclinic, colourless to white, soft at Mohs 2, and builds fibrous aggregates that often pseudomorph the inyoite they replaced.该矿物种属三斜晶系，无色至白色，莫氏硬度仅为 2，形成纤维状集合体，且常成其所交代的水硼钙石的假象。

Discovery and naming

• Meyerhofferite was recognised in 1914 among the borate salts of Death Valley in Inyo County, California, where the Monte Blanco deposit had long been worked for colemanite and ulexite.迈耶霍夫石于 1914 年在加利福尼亚州因约县死谷的硼酸盐中被识别，当地的蒙特布兰科矿床早已因硬硼钙石与钠硼解石而被开采。
• The name honours Wilhelm Meyerhoffer (1864–1906), a chemist at the universities of Vienna and Berlin who worked with Jacobus Henricus van't Hoff on the composition and origin of saline minerals.名称纪念威廉·迈耶霍夫（Wilhelm Meyerhoffer，1864–1906），他是维也纳大学与柏林大学的化学家，曾与范托夫（Jacobus Henricus van't Hoff）合作研究盐类矿物的组成与成因。
• Meyerhoffer was born at Pinsk on 13 September 1864 and died at Merano on 21 April 1906, and it was he who first synthesised the compound in the laboratory rather than the man who found the mineral.迈耶霍夫 1864 年 9 月 13 日生于平斯克，1906 年 4 月 21 日卒于梅拉诺；在实验室里首次合成该化合物的正是他，而非发现该矿物的人。
• The type locality is the Monte Blanco mine in the Black Mountains of the Amargosa Range, Death Valley, Inyo County, California.模式产地为加利福尼亚州因约县死谷阿马戈萨岭黑山的蒙特布兰科矿。
• Type material is held at Harvard University under catalogue number 134572 and at the National Museum of Natural History in Washington under 87237 and 93640.模式标本分藏哈佛大学（编号 134572）与华盛顿美国国家自然历史博物馆（编号 87237 与 93640）。
• The species was described before 1959 and is therefore classed as grandfathered by the International Mineralogical Association, which means it needed no formal re-approval.该矿物种在 1959 年之前即已被描述，故被国际矿物学协会列为沿用原名（grandfathered），无须重新正式批准。
• The 2021 compilation of approved mineral symbols assigned it the abbreviation Mhf.2021 年的批准矿物符号汇编为其分配缩写 Mhf。^[1]

Occurrence and paragenesis

• Meyerhofferite is typically a minor component of sedimentary or lake-bed borate deposits, and it rarely forms beds thick enough to be mapped on its own.迈耶霍夫石通常是沉积或湖底硼酸盐矿床的次要组分，很少形成厚到可单独填图的层位。
• In California it is known from the Monte Blanco deposit, from along Gower Gulch in the Furnace Creek district of Death Valley, and from the Kramer borate deposit at Boron in Kern County.在加利福尼亚州，它见于蒙特布兰科矿床、死谷弗内斯溪区沿高尔奇沟一带，以及克恩县博伦的克莱默硼酸盐矿床。
• Outside the United States it occurs at Mesa del Almo, thirteen kilometres southeast of Magdalena in Sonora, Mexico.在美国以外，它产于墨西哥索诺拉州马格达莱纳东南十三千米的阿尔莫台地。
• In Argentina it has been found at the Anita mine in the Sijes district and in the Tincalayu borax deposit of the Salar del Hombre Muerto, Salta Province.在阿根廷，它见于锡赫斯区阿尼塔矿与萨尔塔省翁布雷穆埃尔托盐沼的廷卡拉尤硼砂矿床。
• Turkish specimens come from many deposits of the Bigadiç borate district in Balıkesir Province and from the Killik and Espey borate mines near Emet in Kütahya Province.土耳其标本来自巴勒克埃西尔省比加迪奇硼酸盐区的多处矿床，以及屈塔希亚省埃梅特附近的基利克与埃斯佩硼酸盐矿。
• The deposit at Inder in Kazakhstan is a further locality, and the mineral is otherwise reported only as scattered occurrences in evaporite sequences.哈萨克斯坦因杰尔矿床是另一处产地，此外该矿物只作为蒸发岩序列中的零星产出而被报道。
• Its constant associates are inyoite, colemanite, hydroboracite and ulexite, the four minerals that define the calcium borate assemblage of these deposits.与之稳定共生的有因水硼钙石、硬硼钙石、水硼钙石与钠硼解石，这四种矿物构成了此类矿床的钙硼酸盐组合。

Crystal structure

• Meyerhofferite is triclinic and acentric, with space group P1 and point group 1, and the cell contains two formula units.迈耶霍夫石属三斜晶系且无对称中心，空间群为 P1，点群为 1，晶胞内含两个化学式单位。
• The cell has a = 6.632(1), b = 8.337(1) and c = 6.4748(6) Å, with α = 90.81(1), β = 101.97(1) and γ = 86.76(1)°, giving a volume of 349.65 ų.晶胞参数为 a = 6.632(1)、b = 8.337(1)、c = 6.4748(6) 埃，α = 90.81(1)、β = 101.97(1)、γ = 86.76 度，体积 349.65 立方埃。^[2]
• Burns and Hawthorne refined the structure in 1993 by single-crystal X-ray diffraction and combined the refinement with structure-energy calculations to locate the hydrogen atoms.伯恩斯与霍桑于 1993 年用单晶 X 射线衍射精修了结构，并把精修结果与结构能量计算结合以定位氢原子。
• The building unit is a three-membered ring of composition [B₃O₃(OH)₅]²⁻, formed by two BO₂(OH)₂ tetrahedra sharing corners with one planar BO₂(OH) triangle.构造单元是组成为 [B₃O₃(OH)₅]²⁻ 的三元环，由两个 BO₂(OH)₂ 四面体与一个平面 BO₂(OH) 三角形共角相连而成。
• Calcium is seven-coordinated in a CaO₃(OH)₄(OH₂) polyhedron, and these polyhedra share edges to build infinite chains that run parallel to the c axis.钙为七配位，构成 CaO₃(OH)₄(OH₂) 多面体，这些多面体共棱连接成平行于 c 轴的无限链。
• A hydrogen-bonding network ties the calcium chains to the borate rings, and it is this network that holds the otherwise loosely connected structure together.氢键网络把钙链与硼酸根环系在一起，正是这一网络使原本连接松散的结构得以维持。
• The species belongs to the inderite group, whose members share the same borate ring and calcium-chain construction with different amounts of interlayer water.该矿物种属因杰石族，族内各成员共享同一套硼酸根环与钙链构筑方式，只是层间水的数量不同。

Physical properties

• Hardness is 2 on the Mohs scale, and the measured density of 2.120 g/cm³ agrees closely with the value of 2.116 g/cm³ calculated from the cell.莫氏硬度为 2，实测密度 2.120 g/cm³ 与由晶胞算得的 2.116 g/cm³ 十分接近。
• Cleavage is perfect on {010}, while traces of parting appear on {100} and {110}no twinning has been observed. 解理在 {010} 上完全，在 {100} 与 {110} 上只留痕迹；未观察到孪晶。
• Crystals are elongated along [001] and usually flattened on {100}, occurring as fibrous divergent or radiating aggregates that are commonly reticulated.晶体沿 [001] 伸长，通常扁平于 {100}，以纤维状发散或放射状集合体产出，且常呈网状。
• Individual crystals reach about 4 cm but are crude, and nodular masses also occur where the mineral replaces inyoite in situ.单晶可达约 4 厘米，但晶形粗劣；在矿物就地交代因水硼钙石之处还会出现结核状块体。
• Pseudomorphs after inyoite are common and keep the shape of the original crystals, which is one of the easiest field criteria for the species.因水硼钙石的假象十分常见，且保留原晶体的外形，这是该矿物种最容易的野外判据之一。
• The strongest powder lines fall at 8.31 and 6.47 Å, both with intensity 100, followed by 4.97 at 25 and 4.15, 3.15, 3.07 and 2.501 Å at 20 each, on ICDD card 12-411 for Monte Blanco material.粉晶最强线位于 8.31 与 6.47 埃，强度均为 100；其后为 4.97 埃（强度 25）以及 4.15、3.15、3.07 与 2.501 埃（强度各 20），数据取自蒙特布兰科材料的 ICDD 12-411 卡。

Optical properties

• The mineral is colourless to white, occasionally pale yellow, with a white streak, a vitreous to silky lustre and transparent to translucent diaphaneity.矿物无色至白色，偶带淡黄，条痕白色，光泽为玻璃至丝绢状，透明至半透明。
• It is biaxial negative, and the measured and calculated values of 2V agree at 78°.属二轴晶负光性，实测与计算的 2V 均为 78 度，两者一致。
• The refractive indices are α = 1.500, β = 1.535 and γ = 1.560, which give a birefringence of 0.060.折射率为 α = 1.500、β = 1.535、γ = 1.560，双折射率 0.060。
• Dispersion is weak and in the sense r > v, so the mineral shows little colour fringing in white light.色散较弱，方向为 r 大于 v，故在白光下几乎不显色边。
• The optical orientation is X at (165°, 62°), Y at (45°30′, 47°) and Z at (−83°, 55°), referred to c and b in the φ and ρ convention.光性方位为 X 位于（165 度，62 度）、Y 位于（45 度 30 分，47 度）、Z 位于（−83 度，55 度），以 c 与 b 按 φ、ρ 约定表示。
• Because the mean index is close to that of Canada balsam at 1.537, grains show almost no relief and their boundaries are hard to see in thin section.由于平均折射率接近加拿大树胶的 1.537，薄片中颗粒几乎不显突起，边界也难辨认。

Formation and alteration

• Meyerhofferite forms mainly by the loss of water from inyoite, and it is therefore a supergene alteration product rather than a primary precipitate.迈耶霍夫石主要由因水硼钙石失水形成，因此属表生蚀变产物，而非原生沉淀。
• The reaction is simply the loss of three water molecules from the tetrahydrate, CaB₃O₃(OH)₅·4H₂O becoming CaB₃O₃(OH)₅·H₂O.反应本身只是四水合物失去三个水分子，即 CaB₃O₃(OH)₅·4H₂O 变为 CaB₃O₃(OH)₅·H₂O。
• That reaction converts a borate with isolated rings and a large interlayer water content into a denser structure in which calcium chains are directly linked by hydrogen bonds.该反应把含孤立硼环与大量层间水的硼酸盐转变为更致密的结构，其中钙链之间由氢键直接相连。
• The kinetics and thermodynamics of the dehydration of inyoite have been measured, which makes the pair a well-constrained natural dehydration couple.因水硼钙石脱水的动力学与热力学已被测定，使这一对矿物成为约束良好的天然脱水序列。^[3]
• Frost and co-workers characterised meyerhofferite by thermal analysis, X-ray diffraction and infrared emission spectroscopy, and followed the loss of water and the breakdown of the borate rings on heating.弗罗斯特等人用热分析、X 射线衍射与红外发射光谱表征了迈耶霍夫石，并追踪了加热过程中水的失去与硼环的崩解。^[4]
• In the Furnace Creek Formation, of Miocene to Pliocene lacustrine facies, borates crystallised as the lake water evaporated and then dehydrated further once the beds were exposed.在属中新世至上新世湖相沉积的弗内斯溪组中，硼酸盐随湖水蒸发而结晶，并在层位出露后进一步脱水。

Uses

• Meyerhofferite has no industrial use, and the borax industry relies on borax itself, colemanite and ulexite instead.迈耶霍夫石没有工业用途，硼砂工业依赖的是硼砂本身、硬硼钙石与钠硼解石。
• Its value is mainly indicative: where it appears, the inyoite of the deposit has begun to dehydrate, which tells the field geologist how far alteration has gone.它的价值主要在指示意义：一旦出现，说明矿床中的因水硼钙石已开始脱水，可据以判断蚀变推进的程度。

Related minerals and varieties

• Inyoite is the parent phase, with the same borate ring but four molecules of water instead of one, and the two are structurally related by a simple dehydration step.因水硼钙石是母相，硼酸根环相同但含水四分子而非一分子，两者在结构上只差一步简单脱水。
• Colemanite, CaB₃O₄(OH)₃·H₂O, is the other common calcium borate of these deposits, but its borate groups are linked into chains rather than isolated rings.硬硼钙石 CaB₃O₄(OH)₃·H₂O 是这些矿床中另一种常见钙硼酸盐，但其硼酸根连成链而非孤立环。
• Ulexite and hydroboracite complete the assemblage, and together with meyerhofferite they record the evaporation path of the original lake brine.钠硼解石与水硼钙石补足了这一组合，它们与迈耶霍夫石一起记录了原湖卤水的蒸发路径。
• In the Strunz-mindat scheme the species stands at 6.CA.30 among the neso-triborates, with Dana number 26.3.2.1 and Hey's reference 9.3.17.在 Strunz-mindat 方案中，该矿物种位于岛状三硼酸盐的 6.CA.30，丹那编号为 26.3.2.1，海氏参考号为 9.3.17。