J. Japan. Assoc. Min. Pets. Econ. Geol. 79, 503-508, 1984

Calcian serandite in a magnesioriebeckite-quartz schist from

the Mitsuishi district, Hidaka Province, Hokkaido

TOSHIRO MORIKIYO

Department of Geology, Faculty of Science, Shinshu University, Matsumolo 390, Japan

Calcian serandite was found in a magnesioriebeckite-quartz schist from Mitsuishi, Hidaka Province, Hokkaido. The schist is composed of magnesioriebeckite, epidote, calcian serandite, albite, aegirine and quartz. Chemical composition and physical properties of the mineral are

presented together with the results of chemical analyses of magnesioriebeckite, pectolite and the host whole rock. The calcian serandite seems to be formed as a primary metamorphic mineral

judging from its mode of occurrence. It is assumed that the appearance or disappearance of the mineral in the crystalline schist depends on the chemical composition of the host rock under the condition of the epidote-glaucophane schist facies. This is the first finding of calcian serandite from metamorphic rocks.

Introduction

Serandite is the manganese analogue of

pectolite, and calcian serandite has an interme

diate composition between pectolite and seran

dite. Pectolite has been already reported as a

vein mineral in the epidote-amphibolite from

the Mitsuishi district, Hidaka Province, Hok

kaido, by Suzuki et al. (1974) and Harada and

Hariya (1984).

In this district, various kinds of metamor

phic rocks are exposed as xenolithic blocks in

the serpentinites as shown in Fig. 1. The

metamorphic rocks are grouped into the follow

ing types: epidote-amphibolite (hornblende+

epidote+albite+chlorite•}muscovite•}gar

net•}biotite), greenschist (actinolite+epidote+

albite+chlorite+muscovite•}riebeckite

•} aegirine•}stilpnomelane•}pumpellyite),

magnesioriebeckite-quartz schist (magnesio

ribeckite+quartz+epidote+calcian seran-

dite+albite+aegirine+magnetite), metagab-

bro (chlorite+albite•}prehnite•}pumpellyite).

From the magnesioriebeckite-quartz

schist, I found calcian serandite. In this paper,

the mode of occurrence, physical properties and

chemistry of the mineral are presented.

Description of the rock samples

Calcian serandite-bearing specimen was

taken from a block on mountain slope 3km

north-northeast of Mitsuishi (1 in Fig. 1). The

rock is dark green and very fine-grained. It is

rather homogeneous, and schistosity or bedding

is not recognized. Original texture such as

clastic or igneous one is not observed, but it

seems to be a kind of ferruginous siliceous

sedimentary rock. Under the microscope, the

rock is composed of magnesioriebeckite,

quartz, albite, aegirine and calcian serandite

with a subordinate amounts of epidote, magnet

ite and clay mineral. Magnesioriebeckite is a

small acicular and columnar crystal with the

size less than 0.01•~0.06mm. Its color is vivid

bule-green to violet. Calcian serandite is an

euhedral and prismatic crystal, and is scattered

(Manuscript received July 9, 1984)

504 Toshiro Morikiyo

Fig. 2. Photomicrograph of calcian serandite from specimen 73081203 in plane light. Bar: 0.1mm. Cs, calcian serandite; Mr,

magnesioriebeckite; Qz, quartz.

Fig. 1. Geological map of the Mitsuishi district and localities of the specimens studied.

1: calcian serandite-bearing rock (specimen 73081203).2: pectolite-bearing rock (specimen

78100801).Compiled after Ishibashi (1939) and Morikiyo (1979).

in the fine-grained matrix composed of

magnesioriebeckite, quartz and albite as seen in

Fig. 2. It is colorless and average grain size is

0.16•~0.04mm. Many tiny inclusions of low

index material, which can not be identified, are

contained, and the periphery of crystal is some

times altered to brown clayey minerals.

Epidote is present but is a very small amount.

Quartz is abundant and shows a saccharoidal

texture. These minerals do not show any reac

tion texture among each other, except for

between calcian serandite and clayey minerals.

Therefore, magnesioriebeckite, quartz, albite,

aegirine and epidote are in equilibrium with

calcian serandite during the metamorphism,

which seems to be in the epidote-glaucophane

schist facies.

Pectolite-bearing rock has been found from

the quarry at the south of Horai-san (2 in Fig.

1). The rock is a dark green medium-grained

epidote-amphibolite and contains large radiat

ing aggregates of pectolite. This consists of

blue-green hornblende, epidote, albite, chlorite,

pectolite, muscovite and pumpellyite with a subordinate amounts of sphene, rutile and

apatite. Pectolite is a colorless large poikilo

blastic crystal with a length of several centi

meters and includes hornblende, albite and

pumpellyite. Aggregates of dull yellowish

green chloritic mineral have been formed along the periphery. Pumpellyite forms aggregates

of wedge-shaped grains and occurs as veinlets.

The original mineral assemblage seems to be

musc ovite-chlorite-albite-epidote-hornblende,

which is for the albite-epidote-amphibolite

facies (Morikiyo, 1979). Pectolite, pumpellyite

and chloritic mineral would be formed in the

later stage of the metamorphism, of which

condition seems to be lower than that of the

albite-epidote-amphibolite facies.

Mineral description and discussion

Calcian serandite was separated from the

other minerals in the powdered sample by

means of the heavy liquids with a centrifuge.

Densities of the heavy liquids were measured

with the specific gravity indicators, and the

Calcian serandite from Mitsuishi district 505

Table 1. X-ray diffraction data

1: Pectolite (Schaller, 1955).

2: Pectolite from Mitsuishi (specimen 78100801).

3: Manganoan pectolite (Schaller, 1955).

4: Calcian serandite (Schaller, 1955).

5: Calcian serandite from Mitsuishi (specimen 73081203).

s: strong, ms: moderately strong, mw: moderately weak.

Experimental condition: CuEa 40kv, 20mA, scanning speed 0.5•‹/min.

densitiy of calcian serandite was measured to

be 3.15•}0.02.

X-ray powder data of calcian serandite

and pectolite are presented in Table 1 together

with the data of Schaller (1955). The data for

pectolite is in good accord with Schaller's data,

and that of calcian serandite from this district

shows an intermediate value between man

ganoan pectolite and calcian serandite by

Schaller.

Refractive indices of calcian serandite

were determined to be ƒ¿=1.641, ƒÀ=1.648,

ƒÁ =1 .675. 2Vz is about 48•‹ and the elongation

is nearly parallel to Z and extinction angle is

usually small.

Calcian serandite and magnesioriebeckite

were chemically analysed as shown in Table 2.

The analytical result of pectolite from locality

2 in Fig. 1 is also presented in Table 2. Atomic

ratios of the minerals were calculated on the

anhydrous basis of O=17 for calcian serandite

and pectolite, and O=23 for magnesioriebeck

ite. Mn/Ca ratio of calcian serandite exceeds

1. There is no compositional difference from

grain to grain. Whether a crystal is chemi

cally zoned or not could not be determined

because of the small size. Pectolite is almost

free from MnO and is very close to the end

member of pectolite. ƒÂD value of this pectolite

has been reported to be -314% by Kuroda

et al. (1979).

Pectolite usually occurs as a hydrothermal

mineral in serpentinites and in dolerites. It is

also reported in alkaline igneous rocks and in

kimberlites. However, it has rarely been re

ported from metamorphic rocks except for

some calcium-rich rocks and skarns (Deer

et al., 1978).

Occurrence of calcian serandite and

serandite is rare and they have been found

mainly from alkaline igneous rocks, such as

nephelin syenite in Greenland (Winther, 1901),

phonolite in Queensland, Australia (Carr and

Phillips, 1976), lujavrite in Lovozero, Kola pen

506 Toshiro Morikiyo

Table 2. Chemical analyses

* EPMA analyses.

** Calculated based on the assumption that Fe+3/Fe+2=1.

Fig. 3. A(Al+Fe+3-3K)-C(Ca)-F(Fe+2+Mn+

Mg)-N(Na) diagram. Abbreviation for

minerals: Pect, pectolite; Cal Ser, calcian

serandite; Ser, serandite; Ab, albite;

Aeg, aegirine; Rie, riebeckite; Gl, glauco

phane; Tr, tremolite; Act, actinolite;

Parag, paragonite; Pump, pumpellyite;

Ep, epidote; Chl, chlorite. Minerals are

indicated by atomic ratios of A-C-F-N.

Star, chemical composition of calcian se

randite-bearing rock. Triangle: calcian

serandite-free riebeckite-quartz schists

and riebeck ite-al bite-epidote-actinolite

schist.

insula (Semenov et al., 1976) and sodalite

syenite in St. Hilaire, Canada (Semenov et al.,

1976; Philpotts, 1974). Recently, pure seran

dite has been reported from the stratiform

manganese ore deposits of the Tanohata mine,

Japan, and its crystal structure has been deter

mined (Takeuchi et al., 1976). Calcian seran

dite has not yet been found from metamorphic

rocks.

Metamorphic minerals, which are common

in the epidote-glaucophane schist facies rocks

are shown in the A (Al+Fe+3-3K)-C(Ca)-

F(Fe+2+Mn+Mg)-N(Na) diagram (Fig.3).

Mineral paragenesis of the calcian serandite

bearing rock is indicated by the triangular

pyramid (Ep-Rie•EGl-Ab• Aeg-Cal Ser)

within the diagram and chemical composition

of the host rock is plotted within the pyramid.

For comparison, chemical composition of

riebeckite-albite-epidote-actinolite schist from

Mitsuishi and that of riebeckite-quartz schist

from other areas of the Kamuikotan

metamorphic belt are also plotted in the dia

gram. These rocks are considered to belong to the epidote-glaucophane schist facies and the

paragenesis, epidote-albite-riebeckite is stable. Chemical composition of calcian serandite

bearing schist is plotted in the N side of the

plane Ep-Ab• Aeg-Rie• Gl, whereas those of calcian serandite-free schists are plotted

between A and the plane. From this figure, it

is considered that the appearance or disappear

ance of calcian serandite depends on the chemi

cal composition of the host rock, especially Na

content under the condition of the epidote

glaucophane schist facies.

Acknowledgements: I would like to

Calcian serandite from Mitsuishi district 507

Table 3. Chemical analyses of whole

1: Calcian serandite-bearing magnesioriebeckite-quartz schist

(Specimen 73081203).2: Riebeckite-bearing albite-quartz schist from Kamietanbetsu

(Suzuki and Suzuki, 1959).

3: Aegirine augite-bearing riebeckite-quartz schist from

Kamuikotan (Suzuki and Suzuki, 1959).

4: Aegirine-bearing riebeckite-albite-epidote-actinolite schist

from Mitsuishi (Ishibashi, 1937).

express my appreciation to Prof. Y. Kuroda of

Shinshu University for helpful suggestions and

critical reading of the manuscript. I am also

grateful to Dr. K. Tazaki of Instiute for Ther

mal Spring Research, Okayama University and

Dr. M. Inomata of Geological Institute, Tokyo

Nogyo Daigaku for their help in the analytical

work.

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508 Toshiro Morikiyo

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北 海 道,日 高 三 石 地 方 の マ グ ネ シ オ リー ベ ッ ク閃 石 片 岩 か ら,

カ ル シ ア ン　 セ ラ ン ダ イ トの 産 出

森 清 寿 郎

北 海道,日 高 三石 地方 の マ グネ シ オ リーベ ック閃 石一 石英 岩 か ら,カ ル シア ン　 セ ラン ダイ トを発 見 し

た。 母岩 は,マ グ ネ シオリ ーベ ック閃石,緑 レン石,カ ル シ ア ン　 セ ラン ダイ ト,曹 長石,エ ジ リン,石

英 な どか ら成 る変成 岩 で,原 岩 は鉄 に比 較的 に富 む珪 質 堆積 岩 と思 われ る。そ の全 岩組 成 は, Alに 対 して

Naに 當 み, Mn量 も比較 的 多 い。 カル シア ン　 セ ラン ダイ トは産 状 か らみ て,緑 レン石一 藍 閃石 片岩 相 の

変成 鉱 物 と思わ れ る。この鉱 物 は,今 ま で アル カリ 火成 岩 か らの み発見 され て いた が,今 回 の発見 に よ り,

変 成岩 中で も母 岩 の化学 組 成 が適 当で あれ ば 出現可能 であ るこ とが判 明 した。