CIPW标准矿物计算

功能简介

The program for CIPW was written by Kurt Hollocher, Geology Department, Union College, Schenectady, NY, 12308, hollochk@union.edu

本程序的CIPW标准矿物计算部分使用了Kurt Hollocher的程序 主要用于火成岩 CIPW 标准矿物计算，适用于基性岩到酸性岩各类岩石。

为方便作图（与散点图程序配套），该程序部分还附带有两组岩石化学参数计算，即 Batchelor 的多阳离子R1－R2 图解中R1和R2和值 和 Pearce 的玄武岩构造环境判别图所用的F1、F2、F3值。

4.2  启 动

见1.4运行 部分

4.3  认识工作窗口（界面）

启动本程序后，程序将在Excel 工作表中添加一个浮动工具栏。

4.4  数据准备

本软件所使用的数据格式如下：

原始数据可存放于任何 Excel 工作薄文件任一表格中，只要它处在活动状态就可计算。

工作表的第一列为样品号，在有效范围内不得有空格，否则空格所在行及其以下的样品不参与计算。

工作表的第一行为变量名，在有效范围内不得有空格。

第二列为岩石类型，该参数对于需要进行 Fe2O3-FeO 校正的岩浆岩是必要的，本软件只识别“火山岩”和“侵入岩”两类，填其它类型或空白则不作铁校正。

从第三列起，变量按下表的习惯顺序排列，顺序不得打乱，也不得跳过；缺项可用空格，也可输入0 值。以下是一个数据格式样表:

4.5  计算

当数据准备好后点击浮动工具栏中的“CIPW标准矿物计算”按钮即可 完成全部计算。计算结果保存在一个新的工作表中。

4.6  保存计算结果

保存结果请用 CIPW浮动工具栏中的“保存 当前工作表选项.。

如果您是用原Excel系统中的有关保存工具保存结果（正常情况下，当“CIPW标准矿物计算结果”工作薄处于活动状态时，系统中的有关保存工具栏和菜单项处于不可用状态），当您再次打开这个结果工作薄时，您会发现，您所打开的只是一个空白表格。应当避免使用原系统的保存工具保存文件。

The CIPW norm is named for the four petrologists, Cross, Iddings, Pirsson and Washington, who devised it in 1931

What is a Norm and Why is it Needed?

A norm is a means of converting the chemical composition of an igneous rock to an ideal mineral composition. It often reveals similarities in rocks that have quite different modes, or observed mineral assemblages. Some of the factors that can cause such variations are:

• Disequilibrium (for example, zoned minerals or reaction rims isolating the interiors of grains)
• Temperature
• Pressure
• Alteration
• Water content (otherwise identical rocks might contain biotite, amphibole, or pyroxene, depending on water content)
• Other minor constituents. For example, excess sulfur or chlorine might cause scapolite to form instead of feldspar. Boron typically causes tourmaline to form.

The CIPW norm calculates mineral composition as if the magma were anhydrous (water is simply treated as a separate phase) and at low pressure. Other more complex norms have been devised for high-pressure or very hydrous situations. In an ideal world, a norm would match the observed mineral phases perfectly. To create such a norm, we would have to understand magma crystallization perfectly (and we don't), and the norm would be extremely complex to calculate.

Logic of Calculation

The logic of calculating a norm is simple even if the steps are tedious. Deal with the simplest and most predictable minerals first, then apply corrections if the rock is silica-deficient.

• Allocate the most predictable elements
  • Allot Common Substitution Elements to Major Elements
    Nickel and manganese are combined with ferrous iron, strontium and barium with calcium.
  • Allot Minor Elements to Accessory Minerals. These include P (Apatite), S, (Pyrite), Cr (Chromite), F, (Fluorite), CO₂ (Calcite) and Zr (Zircon)
  • Allot Titanium to ilmenite or sphene. Later on, Ti may need to be alloted to perovskite or rutile.
  • Allot Calcium and Aluminum to anorthite.
• Provisionally form silica-saturated silicates
  • Provisionally Allot Alkalis and Aluminum
  • Begin Alloting Iron and Magnesium
  • Create Provisional Pyroxenes
  • Silica Excess forms Quartz
  • If there is no silica deficit, calculation is complete.
• Convert Provisional Minerals to Remove Silica Deficit
  • Convert Hypersthene to Olivine
  • Convert Sphene to Perovskite
  • Convert Albite to Nepheline
  • Convert Orthoclase to Leucite
  • Convert Wollastonite and Diopside to Calcium Orthosilicate (Rare)
  • Convert Orthoclase to Kaliophilite (Rare)

Calculating the Norm

Preliminary Comments

• Convert all weight percentages to molecular percentages.
• All quantities are running amounts; that is, use the quantity remaining after any previous calculations.
• Formulas follow common computer program syntax. For example, FeO = FeO + MnO + NiO means sum FeO, MnO and NiO, then replace the value of FeO with the calculated value.
• Provisional calculations are denoted by P*; for example, P*Albite means a provisional quantity for albite, which may be converted later on to nepheline. Any provisional amounts remaining at the end become final amounts.

Allot Common Substitution Elements to Major Elements

• FeO = FeO + MnO + NiO
• CaO = CaO + BaO + SrO

Allot Minor Elements to Accessory Minerals

• Apatite = P₂O₅, CaO = CaO - (10/3)P₂O₅, P₂O₅ = 0
• Pyrite = S, FeO = FeO - S/2, S = 0
• Chromite = Cr₂O₃, FeO = FeO - Cr₂O₃, Cr₂O₃ = 0
• Fluorite = F, CaO = CaO - F, F = 0
• Calcite = CO₂, CaO = CaO - CO₂, CO₂ = 0
• Zircon = ZrO₂, SiO₂ = SiO₂ - ZrO₂, ZrO₂ = 0

Allot Titanium

• If FeO exceeds Titanium then Ilmenite = TiO₂, FeO = FeO - TiO₂, TiO₂ = 0
• If TiO₂ exceeds FeO then:
  P*Sphene = TiO₂, CaO = CaO - TiO₂, SiO₂ = SiO₂ - TiO₂, TiO₂ = 0

Provisionally Allot Alkalis and Aluminum

• P*Orthoclase = K₂O, Al₂O₃ = Al₂O₃ - K₂O, SiO₂ = SiO₂ - 6 K₂O
• If Al₂O₃ exceeds Na₂O then:
  P*Albite = Na₂O, Al₂O₃ = Al₂O₃ - Na₂O, SiO₂ = SiO₂ - 6 Na₂O, Na₂O = 0
• If Na₂O exceeds Al₂O₃ then:
  • Albite = Al₂O₃, Na₂O = Na₂O - Al₂O₃, SiO₂ = SiO₂ - 6 Na₂O, Al₂O₃ = 0
  • Aegerine = Na₂O, Fe₂O₃ = Fe₂O₃ - Na₂O, SiO₂ = SiO₂ - 4 Na₂O
  • In the very rare case where Na₂O is left over due to insufficient Fe₂O₃, allot it to sodium metasilicate. SiO₂ = SiO₂ - Na₂O.
• If Al₂O₃ is left after alloting orthoclase and albite, then:
  Anorthite = Al₂O₃, CaO = CaO - Al₂O₃, SiO₂ = SiO₂ - 2 Al₂O₃, Al₂O₃ = 0
• If Al₂O₃ exceeds CaO in the preceding calculation, then:
  • Anorthite = CaO, Al₂O₃ = Al₂O₃ - CaO, SiO₂ = SiO₂ - 2 CaO
  • Corundum = Al₂O₃, CaO =0, Al₂O₃ = 0

Begin Alloting Iron and Magnesium

• If FeO exceeds Fe₂O₃ then:
  Magnetite = Fe₂O₃, FeO = FeO - Fe₂O₃, Fe₂O₃ = 0
• If Fe₂O₃ exceeds FeO then:
  Magnetite = FeO, Fe₂O₃ = Fe₂O₃ - FeO, FeO = 0, Hematite = Fe₂O₃, Fe₂O₃ = 0
• From here on, all FeO and MgO go to pyroxene plus olivine, but their relative proportions are maintained in all minerals. The sum of MgO plus FeO is designated FM in what follows.

Create Provisional Pyroxenes

• If FM exceeds CaO then:
  • P*Diopside = CaO, FM = FM - CaO, SiO₂ = SiO₂ - CaO, CaO = 0
  • P*Hypersthene = FM, SiO₂ = SiO₂ - FM
• If CaO exceeds FM then:
  • P*Diopside = FM, CaO = CaO - FM, SiO₂ = SiO₂ - 2 CaO, FM = 0
  • P*Wollastonite = CaO, SiO₂ = SiO₂ - CaO

Deal With Silica Excess or Deficit

• If SiO₂ is still positive then: Quartz = SiO₂, SiO₂ = 0, Calculation Finished
• If SiO₂ is negative, then we must convert some of the P*minerals. Call the silica deficit D (D = -SiO₂) and proceed as follows. Whenever D = 0, the calculation is done.

Convert Provisional Minerals to Remove Silica Deficit

Form Olivine

• If D is less than 1/2 of P*hypersthene, then:
  Olivine = D, Hypersthene = P*Hypersthene - 2D, D = 0, Calculation Finished
• If D is greater than 1/2 of P*hypersthene, then:
  Olivine = P*Hypersthene, D = D - 1/2(P*Hypersthene), Hypersthene = 0,

Form Perovskite

• If D is less than P*Sphene, then:
  Perovskite = D, Sphene = P*Sphene - D, D = 0, Calculation Finished
• If D is greater than P*Sphene, then:
  Perovskite = P*Sphene, D = D - P*Sphene, Sphene = 0
• Any excess TiO₂ is accounted as Rutile

Form Nepheline

• If D is less than 4(P*Albite) then:
  Nepheline = D/4, Albite = P*Albite - D/4, P*Albite = 0, D = 0, Calculation Finished
• If D is greater than 4(P*Albite) then:
  Nepheline = P*Albite, D = D - 4(P*Albite), Albite = 0

Form Leucite

• If D is less than 2(P*Orthoclase) then:
  Leucite = D/2, Orthoclase = P*Orthoclase - D/2, P*Orthoclase = 0, D = 0, Calculation Finished
• If D is greater than 2(P*Orthoclase) then:
  Leucite = P*Orthoclase, D = D - 2(P*Orthoclase), Orthoclase = 0

Form Calcium Orthosilicate (Rare)

• If D is less than (1/2)(P*Wollasonite) then: Calcium Orthosilicate = D, Wollastonite = P*Wollasonite - 2D, D = 0, Calculation Finished
• If D is greater than (1/2)(P*Wollasonite) then: Calcium Orthosilicate = P*Wollasonite, D = P*Wollastonite/2, Wollastonite = 0
• If there is still a deficit, convert Diopside to Olivine + Calcium Orthosilicate as follows:
  • If D is less than P*Diopside then:
    Additional Calcium Orthosilicate = D/2, Additional Olivine = D/2. Add these amounts to the previously-formed minerals. Diopside = P*Diopside - D, D = 0, Calculation Finished
  • If D is greater than P*Diopside then:
    Additional Calcium Orthosilicate = P*Diopside/2, Additional Olivine = P*Diopside/2. Add these amounts to the previously-formed minerals. D = D-P*Diopside, Diopside = 0

Form Kaliophilite (Rare)

If there is still a deficit, convert Leucite to Kaliophilite: Kaliophilite = D/2, Leucite = Leucite - D/2, D = 0, Calculation Finished

Convert all remaining provisional minerals, if any, to final quantities

Reference

Myron G. Best; Igneous and Metamorphic Petrology, Freeman, 1982, Appendix E, pp. 616-619

Acknowledgement

Thanks to Dr. Chris McLaren for catching several errors in the original version of this page.

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Created 10 Nov 1997, Last Update 22 November 1999

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